Free tool

Withholding tax & VAT calculator

Work out withholding tax and VAT both ways — forward (from your fee) and reverse (a client withheld 3% = THB X, what was the gross?).

Issue invoices that compute WHT for you →

No credit card required — start on the free plan.

BillsOS only formats and computes documents for you. This is general information, not tax advice — please confirm with the Revenue Department or your accountant.