A Calculator for Money That Has to Reconcile

Floating point is fine until it is a cent

Nearly every calculator computes in binary floating point, where a tenth cannot be represented exactly. Add enough prices and the total drifts — famously, 0.1 + 0.2 comes to 0.30000000000000004. One line item, no problem. A page of them against a bank statement, and you are hunting a cent.

CalcBoard computes in arbitrary-precision decimal. Prices add the way ledgers add, and division carries 15 decimal places before rounding — here is why that differs from everything else.

Rates you set once

Type vat=0.20, tax=0.0825, or markup=1.4 once and use them by name in any panel, in any mode, indefinitely. They persist between sessions, so the rate you use every day stops being something you retype and mistype — more on named variables.

Several figures in view at once

Quoting a job means holding a subtotal, a margin, and a tax figure simultaneously. Invoicing means checking a line against a total. With up to eight panels, each keeping its own expression and history, none of those has to be memorised or written down. Two panels are free; the rest come with the one-time unlock.

A record of what you worked out

• Automatic history. Every calculation is saved — the last 10 free, 500 with Premium.
• Bookmarks and labels. Mark the quote you will need again and name it.
• CSV export (Premium). Copy your history out as CSV and paste it into a spreadsheet.
• Search (Premium). Find the figure you worked out last Tuesday.

Margin and markup are not the same number

The most common small-business arithmetic mistake, and worth stating plainly. On an item costing $60 sold at $100: the markup is (100 − 60) ÷ 60 = 66.7%, while the margin is (100 − 60) ÷ 100 = 40%. Same money, different denominators. Keeping both in adjacent panels is the fastest way to stop conflating them — and the percentage calculator handles either.

Frequently Asked Questions