How to read your Calculus field register
Your field register lists every eInvoice field, where it comes from today and what must change. Start with the To Do List tab.
In short
Your field register is one spreadsheet, built by Calculus staff for your business. It lists every field an eInvoice must carry, where that field comes from on your invoices today, and what must change. Start with the To Do List tab, work through it item by item, and reply to our email with the status of each item.
Why eInvoicing needs it
An eInvoice is not a PDF. It is a structured file that your eInvoicing service provider sends to your customer and reports to the Federal Tax Authority (FTA). Each piece of data sits in its own named field: your Tax Registration Number (TRN), the due date, the VAT category of each line, and so on. If a mandatory field is empty or in the wrong format, the invoice is rejected.
The UAE sets these rules in Ministerial Decision No. 243 of 2025 on the Electronic Invoicing System and Ministerial Decision No. 244 of 2025 on its implementation. The Ministry of Finance explains them in its UAE Electronic Invoicing Guidelines. The data format is the Peppol PINT AE specification. Your register translates all of this into the changes that apply to your own invoices, so you do not have to read the specification yourself.
Most changes are template or master-data changes: a new column, a date field, a code on each customer. Only a few need a change in how you work.
What good looks like
The register has up to six tabs. Here is what each one is for.
| Tab | What it shows | When to use it |
|---|---|---|
| Read Me | What the register is, the colour key and who to contact | Read once, first |
| To Do List | One row per change: what changes on your invoice, and the fixed values or format to use | Start here. This is your work list |
| Field Register | Every eInvoice field, whether it is mandatory or conditional, where it comes from on your current invoice, and whether your system holds it today | When you or your system partner need the detail behind a To Do item |
| Invoice Types & Codes | The document types (tax invoice, credit note, commercial invoice) and the code lists that apply to you, such as VAT categories and credit note reasons | When you need the exact code to put on an invoice |
| Entity Matrix | For groups with several companies: the values that differ per company, such as each one's tax numbers and invoice series | Only if your register covers more than one entity |
| Summary | A count of fields by status | For an overview of how far there is to go |
Each row on the To Do List has a colour. The colour shows the effort, from a quick template change to a process or logic change, such as how you raise credit notes. The Read Me tab gives the full colour key. Do the quick items first: they clear most of the list.
Each To Do item also links to a guide on this site. The guide explains the rule in plain language and shows how to make the change in Tally, in Excel or in another system.
How to reply
Calculus staff send the register with a fit-gap email: one numbered finding per To Do item. Reply to that email with each finding number and one of three answers:
| Answer | What to add |
|---|---|
| Done | Nothing more. A sample invoice that shows the change helps |
| Need help | Tell us your question |
| Don't understand | Tell us what is unclear |
For example: "1 Done. 2 Need help: our Tally does not show a due date field on the invoice. 3 Don't understand: what is a Peppol ID?" A short reply like this is enough. You do not need to finish every item before you reply.
Working through it in Tally or Excel
- Tally users: most items are changes to a ledger, a stock item or the invoice print. Make the change once in the master, then raise one test invoice and check it prints correctly.
- Excel template users: most items are a new column or a fixed list (a dropdown) on your template. Add the column, fill it for one invoice, and send it to us as a sample.
- ERP users: forward the To Do List to your ERP partner. Each row says what the field must hold and in what format.
Checklist
- Read the Read Me tab and the colour key
- Work through the To Do List, quick items first
- Open the linked guide for any item you are not sure about
- Reply to the fit-gap email with each finding number and Done, Need help or Don't understand
- Send a sample invoice once the template changes are in place
The law
- Ministerial Decision No. 243 of 2025 on the Electronic Invoicing System: scope and obligations of issuers and recipients.
- Ministerial Decision No. 244 of 2025 on the Implementation of the Electronic Invoicing System: phases and dates. MoF PDF
- Ministry of Finance, UAE Electronic Invoicing Guidelines, Version 1.1 (1 June 2026). MoF PDF
- Peppol PINT AE specification: the field list behind the Field Register tab. docs.peppol.eu
- Ministry of Finance eInvoicing portal. mof.gov.ae
Common questions
- The register has hundreds of rows. Do I need to read all of them?
- No. Start with the To Do List tab. It lists only the changes you need to make. The Field Register tab is the detail behind each item, for when you or your system partner want to check a field.
- Can we use the data we already hold for existing customers?
- Usually yes. Many fields already sit in your accounting system or invoice template. The Field Register tab shows which ones are in place and which are missing, so you only collect what is new.
- What if we do not understand a finding?
- Reply with the finding number and "Don't understand", and tell us what is unclear. Calculus staff will explain it, or set up a short call to go through it with you.
General guidance on UAE eInvoicing and VAT as they shape the eInvoice. It is not tax advice for a specific transaction. Last reviewed 2026-10-19.
