Invoice series: an independent counter
You can run as many as you need, as long as each one is consecutive within itself. Having several is never the problem: opening a new one every time something goes wrong is.
A group of invoices with its own sequential numbering, usually identified by a prefix.
Article 6.1.a) of the invoicing regulations allows invoices to be issued in separate series where there are reasons that justify it. The justification is broad: different sites, different types of transaction, or simply the year.
The compulsory series
The same article requires a specific series, in all cases, for five situations. The first two are the ones seen every day; the other three, almost never:
- Invoices issued by the customers of the transactions or by third parties, with a different series for each of them.
- Corrective invoices.
- Invoices issued in administrative and judicial enforcement proceedings, under the fifth additional provision of the VAT Regulations.
- Supplies under the reverse charge in article 84.One.2 g) of the VAT Act: silver, platinum and palladium, mobile phones, games consoles, laptops and tablets.
- Intra-group transactions under the advanced form of the special regime for groups of entities (article 61 quinquies.2 of the VAT Regulations).
A scheme that works
A-2026/0001— services invoiced from the office.T-2026/0001— shop sales.R-2026/0001— corrective invoices, compulsory.
Each series starts at 1 and moves on with no gaps. Series T being on 0412 while series A is on 0037 is no problem at all: they are different counters.
What really is a problem
Changing series halfway through the year for no reason, or opening a series “B” to slot in three invoices that were forgotten. A new series is justified by a stable organisational reason, not by a one-off slip. And a forgotten invoice is issued with the date it belongs to, in the series it belongs to, accepting that it is late.
The mistake that comes up most
Putting corrective invoices in the normal series. It is the only one of the five obligations that gets broken daily, and it breaks the count: the main series stops reflecting only transactions and starts mixing in corrections with a negative sign.
Where this carries on in Cairos: Series and numbering in the software.
Terms that go with this one
Almost no tax concept makes sense on its own. These three are the ones that most often turn up beside it.
Sequential numbering
The obligation to number invoices consecutively within each series, with no gaps and no repeats.
InvoicingCorrective invoice
The invoice that corrects one already issued, in its own series and referring expressly to the invoice being corrected.
AccountingRecord book
The compulsory record, in date order, of the invoices issued and received, which underpins the self-assessments and the annual summaries.
This, handled without thinking about it
Cairos keeps the invoices, the record books and Hacienda's forms from the same data, so the theory on this page turns into boxes that are already filled in.
No card and no minimum term.