Invoice numbers: what do the rules actually require?
The invoice number is small but critical. Here's what Swedish bookkeeping law actually requires.
The rules in brief
Under Swedish bookkeeping law, every invoice must have a unique number in an unbroken sequential series. The number must never repeat or be reused: even if an invoice is voided or credited, that number is considered used and is not recycled for the next invoice. The series should normally rise without gaps, but a single gap does not by itself make the bookkeeping incorrect as long as it can be explained. What is actually prohibited is reusing a number or running multiple series at once.
Common mistakes
The most common mistake is running multiple number series at once, for example one per customer, which breaks the requirement for a single sequential series. Another frequent issue is manually losing track after a gap in invoicing and accidentally reusing an old number.
How to avoid the mistakes entirely
Invoicing software tracks the next available number automatically and guarantees it can never be reused or duplicated, no matter how many invoices you create or how long it's been since the last one.
Vanliga frågor
Can I restart at number 1 every year?
No, in Sweden invoice numbers must follow an unbroken sequential series. There's no requirement to reset it yearly, and doing so risks creating duplicates.
What if I accidentally skip a number?
A single gap in the series doesn't make the bookkeeping incorrect as long as it can be explained, for example an invoice that was created but never sent. What's actually not allowed is reusing a number that has already been used.
Does the number have to be purely numeric?
No, you can use a prefix, for example "2026-001", as long as the series stays sequential and unique.
Let invoice numbering take care of itself
FakturaKlar always suggests the correct next number, guaranteed unique.
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