Basics·DE

Invoice number series

How Accountix assigns invoice numbers - one series per company, formats with year and prefix, gap fillers, and what happens on import.

Updated: 27 August 2026·2 min read

What is a number series?

A number series (Rechnungskreis) is the rule your invoice numbers follow: prefix, separator, year, running counter. Every company (issuer) has at least one series of its own - invoice numbers must be unique and sequential per company, not across the whole system.

Format examples:

The counter

Each series keeps a counter. When you create an invoice, Accountix reserves the next number atomically - two people creating invoices at the same moment can never collide. If a number is already taken (for example by an import), the counter skips it on its own.

Fixed numbers and gap fillers

When creating an invoice you can also set the number explicitly. The counter stays untouched - this is how you deliberately fill gaps in the history (say, after a deleted invoice whose number should be reissued). When deleting an invoice, Accountix offers to roll the counter back to the highest remaining number.

Importing existing invoices

When you import an existing PDF invoice it keeps the number printed on it and is only filed under a series. If the imported number matches the series' own format, Accountix advances the counter automatically: after importing RE-0042, the next new invoice becomes RE-0043 - not RE-0031 just because that is where the counter happened to stand. Numbers in a foreign format (from a previous system) leave the counter alone.

Recommendations

• One series per company is usually enough. Multiple series pay off when you want separate sequences (for example domestic/foreign).
• A year in the format (YY or YYYY) makes numbers self-explanatory and prevents mix-ups across years.
• Never reuse a number while the original invoice exists - the series prevents this automatically.