# finance.tax.add-vat
Returns the whole breakdown, not just the tax. An invoice needs net, tax and
gross together, and deriving the third from the other two in caller code is
where rounding bugs are born.
The date is the date of supply. Defaulting it to today is the single most common
way to get a credit note wrong.
## Before you rely on this
**Not professional advice.** This capability calculates tax figures from published rules. It is a software component for developers, not tax advice. Rules change and every rate here has an effective date. Check that the dates cover your case. Verify results against the official sources listed above, and have a chartered accountant or tax adviser review how you use it, before anyone relies on the output. Provided "as is" under its licence, without warranty.
**Unreviewed.** This capability's implementations agree in every language and pass its published test vectors, which were worked out from the official sources cited. But no qualified chartered accountant or tax adviser has yet checked those vectors, or confirmed that the capability covers the cases it claims. Treat it as a draft. Do not use it for real people, money or decisions without your own expert review. Once a qualified reviewer signs off, this notice is replaced with their name, qualification and the date. Each new version needs fresh sign-off.
1.0.1 marks it unreviewed. The code and the tests are unchanged.