Hi,

To preserve historical accuracy of past transactions, you should avoid editing the existing 15% VAT tax. Instead, go to Accounting > Configuration > Taxes, find the current “VAT 15%” tax, and duplicate it. In the duplicated record, update the name to something like “VAT 15.5%”, set the rate to 15.5%, and ensure the Tax Scope (e.g., Sales, Purchases) matches the original. Then, assign it to the same tax group (such as “VAT”) so that your tax reports remain consistent and consolidated. This approach allows you to continue using the old 15% tax for historical documents while switching to the new rate from 1 May 2025 onward.

Hope it helps