Why TermCalc
- Free forever — every tool works without an account, a paywall or a watermark.
- Private by design — everything runs in your browser; no invoice data or numbers are ever uploaded.
- Built for small business — payment terms, working days, VAT and sales tax, margins and markups: the maths you actually do every week, in one place.
Start with the most popular tool: the invoice due date calculator — tell it the invoice date and terms, get a calendar answer in seconds. Sending the invoice next? The invoice generator prints a clean PDF in one click.
The maths most people get wrong
Each calculator on this site exists because a specific mistake happens constantly in real businesses:
- "Net 30" read as working days when it means calendar days — a 10-day difference that turns a healthy cash flow into a crunch. The due date calculator supports both, and writes the exact calendar date.
- Markup quoted when margin was meant — a "50% markup" is only a 33.3% margin, and pricing decisions built on the wrong one quietly undercharge. See both at once on the profit margin calculator.
- VAT removed by subtraction — taking 20% off a gross figure understates the tax, because VAT was calculated on the smaller net. Divide by 1.2 instead; the VAT calculator shows both routes.
- Stacked discounts added — 20% off then 25% off is 40% off, not 45%. The discount calculator multiplies correctly.
Every page explains its formula and links the primary source it came from — OPM for the federal holiday calendar, GOV.UK for VAT rates, FTC rules for pricing claims — so you can check our working, not just our answer.