Published:
23 June 2023
Updated:
23 December 2025
Contents
If there are any words or acronyms in this document that are unfamiliar you can visit the Jargon Buster or use the search tool on the Northern Ireland Customs & Trade Academy (NICTA) website to find a definition.
Introduction
The purpose of this guide is to assist with the decision to use and subsequently complete Periodic Declarations, submitted via the Trader Support Service (TSS) for goods movements from Great Britain (GB) to Northern Ireland (NI).
Periodic Declarations are a method of declaring goods under combined Supplementary Declarations. This process reduces the burden of submitting individual Supplementary Declarations by creating a single Periodic Declaration when you make multiple goods movements over the same calendar month. Consignment (header) level information does not have to be provided repeatedly for Supplementary Declarations that have been combined in one Periodic Declaration. This is permitted as a trade simplification under Title V of the Union Customs Code (UCC), to improve efficiency in the customs process.
The TSS simplified journey allows businesses to move goods from GB to NI by making a simplified declaration before the goods move and then providing the full information about the goods after they have moved. As part of this journey, TSS provides a service to help users identify appropriate Supplementary Declarations and amalgamate these into a Periodic Declaration for the relevant month.
No specific authorisation is required for businesses to be able to use Periodic Declarations. All users of TSS can choose to use Periodic Declarations if appropriate.
Note: Customs agents (also known as Agents and Intermediaries) may complete declarations in TSS on behalf of traders, if authorised, and should follow the process in this guide after logging into their agent account and selecting ‘Represent a Trader’. Details on how to represent a trader in TSS can be found in A Handbook for Customs Agents and Intermediaries on NICTA.
You can submit more than one Periodic Declaration per month. Any draft Supplementary Declarations that you do not combine into Periodic Declarations should be submitted individually in TSS, as explained in the Supplementary Declarations: Step-by-step guide on NICTA.
This guide leads you through the conditions and restrictions for opting to use Periodic Declarations and the steps you need to follow.
Periodic Declarations in TSS
Where matching rules are met, it is possible to make a monthly Periodic Declaration that combines Supplementary Declarations for multiple consignments for different goods, moved several days apart, into a single Periodic Declaration.
TSS applies matching rules at the consignment (header) level, to help you to determine which open Supplementary Declarations can be combined within a Periodic Declaration.
Note: For the purposes of this guide, open Supplementary Declarations are those in ‘Draft’ or ‘Trader Input Required’ state.
It is important that you fully understand how to interpret and apply these rules, since TSS can’t confirm all criteria that must be met to combine Supplementary Declarations.
When can you use Periodic Declarations?
Goods movements being combined and declared on a single Periodic Declaration must meet the matching rules. Note: These rules differ from the aggregation rules to be met under customs simplified procedures.
You CAN:
- Only add Supplementary Declarations that satisfy the matching rules
- Only combine Supplementary Declarations created in TSS during the same calendar month (1st – 31st)
- Only add Supplementary Declarations that are open (in ‘Draft’ or ‘Trader Input Required’ state). The Data guide: TSS declaration data requirements on NICTA explains how to upload a Periodic Declaration
You CAN’T:
- Create a Periodic Declaration from a Supplementary Declaration that has gone through the TSS Assisted Completion Service
- Create a Periodic Declaration from a Supplementary Declaration for which the first day of the arrival date and time is more than 365 days ago
- Add Periodic Declarations to another Periodic Declaration
- Add Supplementary Declarations for which the first day of the arrival date and time is more than 365 days ago
- Combine Supplementary Declarations if the total number of line items will exceed 99
Validation will be performed within TSS on Supplementary Declarations to check there are no system constraints on the item lines or the consignment (header) level information according to the matching rules. TSS, however, is unable to confirm whether the matching rules have been met and therefore it is important that those intending to make use of Periodic Declarations fully familiarise themselves with these matching rules.
How to combine Supplementary Declarations into a Periodic Declaration
Creating a Periodic Declaration
An Add to Periodic Declaration button is available on the bottom left hand side when you work with Supplementary Declarations in a ‘Draft’ or ‘Trader Input Required’ state that are less than 365 days old.
This button is not displayed for:
- Supplementary Declarations being processed via the Assisted Completion Service
- Supplementary Declarations where the first day of the calendar month of the goods arrival date is more than 365 days ago
- Periodic Declarations
Clicking this button opens a form for combining Supplementary Declarations into a Periodic Declaration.
The blue banner highlights important guidance on consignment (header) level details when combining Supplementary Declarations into Periodic Declarations. You should familiarise yourself with the requirements before proceeding by acknowledging the matching rules indicated in this guide.
If this is the first Periodic Declaration you create in a particular month, or TSS is unable to find any existing Periodic Declarations that meet the matching criteria based on what is in the Supplementary Declaration, a pale blue notice will appear at the bottom of the screen instructing you to click Submit to create a new Periodic Declaration.
When you press Submit, a pop-up will appear confirming the Supplementary Declaration will be incorporated into a new Periodic Declaration and asking you to confirm the declaration meets the criteria for inclusion. It is your responsibility to check compatibility with the matching rules before continuing.
You can Cancel at this stage and no further action will be taken. Otherwise, press OK to proceed with creating a new Periodic Declaration.
Adding one or more Supplementary Declarations to a Periodic Declaration
You can choose between two different methods to add one or more Supplementary Declarations on a Periodic Declaration:
- From the Periodic Declaration
- From the Supplementary Declaration
Method 1: From the Periodic Declaration
Scroll down the Periodic Declaration form and click the Add More Declarations button at the bottom of the screen.
This will open a new form.
Clicking the Supplementary Declaration(s) field opens a drop-down list of the Supplementary Declarations that TSS has proposed meet the matching rules for the Periodic Declaration you wish to combine them with:
For each you will see:
- The Local Reference Number: the Supplementary Declarations that satisfy the matching rules
- Tax Point Date: the Entry Summary Declaration’s arrival date
- The Trader Reference: a free-text field, populated in the Entry Summary Declaration, to create a clear audit trail
- The number of line items for each Supplementary Declaration
When you select one or more of the Supplementary Declarations and click Submit, a pop-up information box asks you to confirm the matching criteria, with the option to press Cancel or press OK to proceed.
Note: You should only combine the additional Supplementary Declarations with the selected Periodic Declaration if you are sure that they adhere to the matching rules for doing so.
After clicking OK, the chosen Supplementary Declarations are integrated into the Periodic Declaration. You can now see the newly added Supplementary Declarations listed under the new ‘Included Supplementary Declarations’ heading in the Goods Records tab.
Note: All Included Supplementary Declarations are now in the state of ‘In Periodic’ and can no longer be changed in the Supplementary Declaration form as they have been incorporated into the Periodic Declaration:
If you wish to remove a Supplementary Declaration from a Periodic Declaration, you have an option to Revert to Non-periodic and start the process again.
You can repeat the process described above for combining more Supplementary Declarations with a Periodic Declaration multiple times (depending on the number of declarations meeting the matching criteria).
If preferred, you can add more than one Supplementary Declaration to a Periodic Declaration at a time by clicking on each of the selected Supplementary Declarations separately in the drop-down list before pressing Submit.
The individual Supplementary Declarations you have selected are then shown in the *Supplementary Declaration(s) field at the bottom of the screen’.
The Total number of Goods Lines field for the Periodic Declaration is updated in accordance with the number of item lines in each Supplementary Declaration that you add.
A new box at the bottom of the form counts the number of Good Lines already in the Periodic Declaration, how many lines are being added when selecting each new Supplementary Declaration, and how many lines remain available to add.
Below the tracking there is a two-column table listing the Supplementary Declarations selected and the Goods Lines included in each, which allows you to see the most appropriate Supplementary Declaration to remove should you begin to approach the Goods Line Limit.
If the combined total exceeds the Goods Line Limit of 99 a pop-up message will be displayed warning you that the last Supplementary Declaration that you have tried to add would take you over the maximum goods permitted under a Periodic Declaration. When you click OK or close this message this last Supplementary Declaration will be removed from the list of Supplementary Declarations in the Goods Count table.
After doing this, the selected Supplementary Declaration will also be removed as a selection in the Supplementary Declaration(s) multi-select field.
Method 2: From the Supplementary Declaration
Go to the Supplementary Declaration you wish to add to a Periodic Declaration and click on the Add to Periodic Declaration button:
This opens a new form titled ‘Add Supplementary Declaration to Periodic Declaration.
If no matching Periodic Declaration exists, you will be offered the opportunity to create one.
Once you press Submit and confirm on the pop-up message you are returned to the starting Periodic Declaration, where the records will have been updated in accordance with the Supplementary Declarations you have just added.
As one of the Periodic Declaration matching rules is that the Tax Point Date of the Supplementary Declaration must be the same month and year of the Periodic Declaration, TSS will take the latest date of the included Supplementary Declarations for updating in the Periodic Declaration.
Additionally, TSS sets the Period Declaration – Calendar Month field to ‘Month – Year’ based on the Tax Point Date of the latest source Supplementary Declaration:
Mixed Exporters
It is possible to mix Supplementary Declarations covering movements from different Exporters under the same Periodic Declaration.
When applicable, TSS will accept an XI EORI number in the Exporter EORI field (item level) on a Periodic Declaration, so you can use compliant XI EORIs.
In instances where the Exporter Address Required / EORI Unknown option was selected in the Entry Summary Declaration of the original Supplementary Declaration(s), there is still the option to populate the Exporter information directly into the Periodic Declaration by checking the Exporter Address Required / EORI Unknown box at the item lines and then manually filling the fields:
- Exporter Name
- Exporter Street and Number
- Exporter City
- Exporter Postcode
- Exporter Country
Matching rules for combining Supplementary Declarations within a Periodic Declaration
It is only possible to combine Supplementary Declarations in a ‘Draft’ or ‘Trader Input Required’ state on Periodic Declarations in TSS if they meet the matching rules below.
The matching process is undertaken at consignment (header) level of the Supplementary Declaration against any available open Periodic Declarations to establish if the Supplementary Declaration can be added to an existing one or if a new Periodic Declaration will have to be created.
It is essential for you and your customs intermediary to have a thorough understanding of the matching rules and to be able to apply them.
To enable Supplementary Declarations to be included, TSS must find a match in the below fields at the consignment (header) level. More information on each field can be found in the Data guide: TSS declaration data requirements on NICTA.
| TSS Field | Data Element | Notes |
| Which type of declaration do you intend to make? | 1/1 | Select from the options in the drop-down list. The entry must be the same for each of the Supplementary Declarations being added. |
| Importer EORI | 3/16 | Combination is only possible where the same EORI is used. |
| INCOTERMS® | 4/1 | Can’t combine different delivery terms on a single Periodic Declaration. |
| Location of goods | 5/23 | Combination is only possible where the same port is used. |
| Type of Movement | 7/4 | Combination is only allowed for movements under the same mode of transport. |
| Destination Country | 5/8 | All goods must be destined for the same country or territory. |
| Tax point date | Must be within the same calendar month (1st – 31st). | |
| Importer Parent Organisation EORI | 3/20 | You can’t combine Supplementary Declarations with different Importer Parent Organisation EORI numbers entered in the Parties at Consignment (header) level. |
| Documents, certificates, and authorisations | 2/3 | You can’t combine Supplementary Declarations with both GB and XI authorisation references under Document Codes C512 or C514. Combination is only possible where all associated Supplementary Declarations use a GB reference, or an XI reference. |
| Representation Type | 3/21 | You can’t combine Direct and Indirect representatives in the same Periodic Declaration. This means that special procedures and standard procedures can’t be mixed. For example, if a procedure requires that the Trader’s own Simplified Customs Declaration Process (SCDP), formerly known as Customs Freight Simplified Procedure (CFSP), be used on the Supplementary Declaration, it cannot be incorporated into a Periodic Declaration with Supplementary Declarations using the TSS SCDP authorisation. |
| Any Holder of Authorisation entry EORI | 3/39 | You can’t combine items on a single Periodic Declaration if the holder of any authorisations on the Supplementary Declarations differs. |
| Supervising customs office | 5/27 | All items on the declarations must have the same Supervising Customs Office. |
| Goods domestic status | NIDOM (UK domestic status goods) and NIIMP (Non-UK domestic status goods) can’t be mixed on a Periodic Declaration. | |
| Use Postponed VAT Accounting | 3/40 | Supplementary Declarations can only be combined if they either all use Postponed VAT Accounting (PVA) or do not use PVA. Usage can’t be mixed on the Periodic Declaration. Additionally, Onward Supply Relief and PVA can’t be mixed in a Periodic Declaration. |
Note: Following the UK’s departure from the European Union (EU), businesses require an EORI number to move goods between GB and the EU. Depending on your location and the specific role you perform in the process of moving goods to NI, you may also require a valid XI EORI number. You can find further information on GOV.UK: https://www.gov.uk/eori/eori-northern-ireland
The matching criteria set out in the above table will consider GB/XI EORI references for the respective association of Supplementary Declarations under a Periodic Declaration.
The following checks are also performed by the TSS system:
Declaration types
You can’t mix Supplementary Declarations originating from different declaration types. For example, a Supplementary Declaration for a Controlled Goods movement, cannot be combined with the Supplementary Declaration for a non-controlled goods movement.
Total number of Goods lines
Only Periodic Declarations where the number of goods lines is less than or equal to 99 minus the number of goods lines on your draft Supplementary Declaration will be suggested in the matching drop-down list. This is so that you avoid exceeding the goods line limit when adding a new Supplementary Declaration to the Periodic Declaration.
Since Supplementary Declarations are still in a ‘Draft’ state at this point and awaiting further information from you, there are limits to the scope of automated checks TSS can carry out.
Although TSS automatically performs matching determination according to system logic, the responsibility for checking conformity before submitting a Supplementary Declaration to a Periodic Declaration remains with you and your customs intermediary.
You should not attempt to attach a Supplementary Declaration to a Periodic Declaration if any of the listed consignment (header) level information does not match.
Reviewing and editing a Periodic Declaration
It is possible to identify Periodic Declarations in the TSS Portal by viewing the column named ‘Periodic Declaration – Calendar Month’ via the All SUP Declarations filter on the Declarations screen.
If this column is populated with a month and year, for example ‘03 – 2023’, then the line relates to a Periodic Declaration.
If no date is in this field, this means the declaration is an ‘ordinary’ Supplementary Declaration.
To view individual Periodic Declarations, click through the Local Reference Number links.
Periodic Declarations look very similar to a standard Supplementary Declaration, but there is no option to select Assisted Completion or to display Previous Movement Information at the top of the form.
New Periodic Declaration form
- The Previous Movement Information is not displayed. To see the previous movement detail select the Included Supplementary Declaration tab and click through to the desired Supplementary Declaration
- Assisted Completion is not available for Periodic Declarations
- There is an additional field called Period Declaration – Calendar Month, which is populated from the Tax Point Date. This field is important as it indicates you are looking at a Periodic Declaration and not just a Supplementary Declaration
There is now a heading for Included Supplementary Declarations in the Goods Records tab that shows which Supplementary Declarations are incorporated under this Periodic Declaration’
The Included Supplementary Declarations heading lists all the associated Supplementary Declarations sorted according to the goods movement date, from oldest at the top to newest at the bottom.
The key characteristics are displayed:
- Local Reference Number – the LRN of the Supplementary Declaration that was consolidated
- SFD Consignment Reference – the LRN of the original Simplified Frontier Declaration which was converted into the Supplementary Declaration included in the Periodic Declaration
- Goods Domestic Status – NIDOM (UK domestic status goods) or NIIMP (Non-UK domestic status goods)
- Tax Point Date – the tax point date of the Supplementary Declaration
- Goods Lines – the number of goods lines on the original Supplementary Declaration that was consolidated.
By clicking into each included Supplementary Declaration individually, you can review the full details. Supplementary Declarations added to a Periodic Declaration can be accessed through the Included Supplementary Declarations list on the Periodic Declaration.
In the new Periodic Declaration itself you will see that all the item lines in the Goods Records tab have been copied across from the Supplementary Declaration(s) into the Periodic Declaration.
The Header Previous Document records are slightly different, however, as not all records are copied from the Supplementary Declaration.
How to Revert to Non-Periodic status or Cancel a Periodic Declaration
When reviewing a Periodic Declaration or in the process of editing, you may need to remove a Supplementary Declaration that you have added to a Periodic Declaration.
Before adding Supplementary Declarations to a Periodic Declaration, you can remove any selected Supplementary Declarations by clicking the × next to the relevant Supplementary Declaration reference number.
However, if the Supplementary Declaration has already been combined into a Periodic Declaration, you should click the Revert to Non-Periodic button in the bottom right hand corner of the Periodic Declaration form to remove the Supplementary Declaration(s)
Note: Taking this step removes all the Supplementary Declarations that have been consolidated into the Periodic Declaration and can’t be undone.
When Supplementary Declarations are removed from a Periodic Declaration, they will return to their original state of ‘Draft’ or ‘Trader Input Required’.
If you opt to use the Revert to Non-Periodic button, you will receive a warning notification, with OK and Cancel buttons:
Clicking OK will:
- Return each of the selected Supplementary Declarations to the ‘Draft’ state. They will no longer be in the ‘In Periodic’ state
- Remove any reference to the Periodic Declaration from the selected Supplementary Declarations (this means that when viewing the Cancelled Periodic Declaration there will be no associated Supplementary Declarations)
- Change the entire Periodic Declaration to the ‘Cancelled’ state
It is very important to understand that the Revert to Non-Periodic button will take each of the Supplementary Declarations associated with the Periodic Declaration back to the original state of ‘Draft’ or ‘Trader Input Required’ and any changes you may have made while editing the Periodic Declaration will be lost.
I need to know more
There are additional guides available on NICTA to support you with trade into and out of Northern Ireland:
- How to use the TSS Portal
- Data guide: TSS declaration data requirements
- Supplementary Declarations: Step-by-step guide
- If your Supplementary Declaration cannot be processed due to an error, see the relevant section in the Guidance on resolution to common error codes for Supplementary and Full Frontier Declarations for instructions on how to resolve the most common errors
You can also consult the TSS Contact Centre for support on 0800 060 8888.
Changes to guidance and policy
Last updated December 2025.
December 2025: Updated for accessibility
March 2025: Updates in reference to Windsor Framework Terminologies and Portal changes.
November 2024: Updates to references of CFSP to SCDP.
January 2024: Updates on XI EORI.
June 2023: Guide published.
Terms used in this guide refer to the terminology used on the TSS Portal. These may not match the most recent terms used on GOV.UK, in HMRC’s Customs Declaration System or the Northern Ireland Online Tariff on GOV.UK.