Free Business Calculators
Instant VAT, GST, late payment interest, and invoice due date calculators. No sign-up required.
All calculators
Seven free tools for freelancers and small businesses in the UK, South Africa, and Australia.
UK VAT Calculator
Add 20% standard rate VAT to a net amount, or extract VAT from a gross price. Shows net, VAT, and gross totals instantly.
Open calculator →South Africa VAT Calculator
Add 15% VAT to a net amount or remove VAT from a gross price. Covers SARS standard rate for SA freelancers and businesses.
Open calculator →Australia GST Calculator
Add 10% GST to a net amount or remove GST from a gross price. Uses the ATO 1/11 rule for accurate GST extraction.
Open calculator →Late Payment Interest Calculator
Calculate statutory interest at Bank of England base rate + 8%, plus the fixed compensation fee (£40, £70, or £100) under the Late Payment of Commercial Debts Act 1998.
Open calculator →UK Late Payment Interest Calculator (by date)
Enter the invoice due date and payment date to work out statutory interest and the fixed compensation fee, with the correct half-year reference base rate selected automatically.
Open calculator →South Africa Late Payment Interest Calculator
Calculate mora interest on an overdue invoice at the prescribed rate of interest (repo rate + 3.5%), or your own contract rate, from the due date and payment date.
Open calculator →Invoice Due Date Calculator
Enter an invoice date and payment terms (Net 7, Net 14, Net 30, Net 60, Due on receipt, or custom) to get the exact due date.
Open calculator →Why free calculators?
Tidybill handles VAT calculations, due dates, and late payment tracking automatically as part of the invoicing workflow. These standalone calculators exist for the moments when you need a quick answer without opening an invoice: checking a client quote, confirming a gross price, or working out how much interest you can claim on an overdue debt.
Each calculator is a single HTML page with no dependencies and no tracking beyond standard page analytics. They work on any device, including mobile.
About the tax rates used
UK VAT: 20% standard rate, as set by HMRC. South Africa VAT: 15%, as set by SARS (in effect since 1 April 2018). Australia GST: 10%, as set by the ATO (in effect since 1 July 2000). UK late payment interest: Bank of England base rate plus 8 percentage points, as required by the Late Payment of Commercial Debts (Interest) Act 1998, with the base rate held at 3.75% through 2026 (statutory rate 11.75%). South Africa late payment interest: the prescribed rate of interest, currently 10.5% (repo rate 7.0% plus 3.5%), effective 1 July 2026. All rates are editable and were checked in July 2026.
Automated invoicing with Tidybill
If you invoice clients regularly, these manual calculations can be automated. Tidybill applies VAT at the correct rate to each invoice line item, calculates due dates from your payment terms, and tracks overdue invoices with automated reminder emails. See Tidybill pricing - free plan available for up to 5 invoices per month.
Start invoicing with Tidybill
Automated VAT invoices, due date tracking, and late payment reminders. Free plan available, no credit card required.
Start invoicing with Tidybill - free plan available