Billkeep
Three calculators, no sign-up
Each of these runs the same arithmetic Billkeep uses on a real invoice — the same engine file, imported unchanged. Nothing is stored, nothing is sent anywhere, and there is no email box at the end.
Pick one
Invoice total calculator
Lines, quantities, discounts and several taxes at once. Shows the breakdown a customer would see, and proves the parts add up to the whole.
Late payment calculator
How many days late an invoice is, and what interest that comes to at a rate you choose. Simple or compounded daily.
Payment link to QR
Turn a Stripe, PayPal or bank link into a QR code you can put on an invoice, and download it. Checked and read back before you get it.
They are the product, with the record-keeping taken out
Every one of these imports core.js — the same file the app
runs. A calculator that reimplemented the arithmetic would eventually
disagree with the product it is advertising, and somebody would find
out while holding an invoice.
- Money is a whole number of pennies, cents or paise. No floating point.
- Tax rates are held to a millionth of a percent, so 9.975% is exact.
- Per-line figures always sum to the total — the calculator shows you that they do.
- Ask for an email address
- Store what you typed, anywhere
- Send anything to a server — the arithmetic happens in this tab
- Claim to know your tax rate, your interest entitlement or your contract
They work with no connection once the page has loaded, like the rest of Billkeep.
The calculator, but it remembers
Billkeep is these sums with a client attached, a number allocated, a document to send, and a record of who has paid.