Variable Symbol and Invoice Numbering 2026

## What a variable symbol is A variable symbol (VS) is a numeric payment identifier that the bank uses to match an incoming payment to a specific document. It has a maximum of **10 digits** — numbers only, no letters, spaces or dashes. The bank will reject or automatically shorten a longer or non-numeric VS, and the payment then won't be matched. ## Why the invoice number is used as the VS Established practice is to set the **VS the same as the invoice number**. When paying, the client copies the VS from the invoice, and you (or your accounting software) then automatically assign the payment to the specific document using that same number — no manual tracking of who paid for what. The invoice number thus plays a double role: it identifies the document in your records as well as the payment on the account. ## The number series must be continuous Number invoices in one unbroken series — no gaps, no skipping, and no deleting issued numbers afterwards. If you cancel an invoice or a customer withdraws from an order, the number **must not be freed up for another invoice** — you issue a corrective tax document (credit note) referencing it, and the number series stays intact. For VAT payers, the tax document's reference number is one of its mandatory requirements under § 29(1)(e) of Act No. 235/2004 Coll., on Value Added Tax. For VAT non-payers, the law doesn't explicitly prescribe this, but a continuous record is the basis for defending your revenue during an audit — see [VAT return](/dane-osvc/priznani-k-dph) and [common self-employed mistakes](/dane-osvc/caste-chyby). You'll find a detailed overview of all mandatory invoice details in the article on [invoice requirements](/fakturace-osvc/nalezitosti-faktury). ## What number format to choose Two formats are most common: - **2026001, 2026002, 2026003…** — year + three digits, suitable for up to roughly 999 invoices a year. - **20260001, 20260002…** — year + four digits, with headroom for thousands of documents a year. Both formats have 7–8 digits, so they easily fit within the 10-digit limit for a variable symbol. At the start of each calendar year you restart numbering from the first sequential number — only the year changes at the beginning.

## Setting up the series at the start of the year In most invoicing tools (e.g. iDoklad or Fakturoid — see the comparison [iDoklad vs. Fakturoid](/nastroje/idoklad-vs-fakturoid)) you enter the number format and starting value once at the start of the year, and the software then generates further numbers automatically and watches the continuity of the series for you. You'll find an overview of other tools in the [comparison of invoicing software](/nastroje/fakturacni-software-srovnani). ## Multiple series for different types of document For clarity, it's common to keep separate number series by type of document, each with its own counter: - **Regular invoices** — e.g. 2026001, 2026002… - **Advance invoices** — e.g. ZF2026001, ZF2026002… - **Corrective documents / credit notes** — e.g. OD2026001, OD2026002… This way the series never overlap, and you can tell the document type right from the prefix. The guide [how to issue an invoice](/fakturace-osvc/jak-vystavit-fakturu) describes how to practically issue an invoice step by step. ## Check before sending Before sending an invoice, verify in the software that the proposed number actually follows on from the last document issued — manual number edits, for example when correcting a mistake, are the most common cause of gaps in the series.