Fair maths

We count in whole pennies

Computers are famously bad at decimals — ask one for 0.1 + 0.2 and you’ll get 0.30000000000000004. So Tot Up never does that kind of maths on your money. Every amount is stored and added up as whole pennies: £73.42 is 7,342 pennies, and 7,342 is a number a computer never gets wrong. Rounding only ever happens once, in the open, where you can see it — which brings us to the odd penny.

The odd penny goes to someone — and we say who

Sam pays £10.00 for breakfast, split equally between three people. That’s £3.33 each — with a penny left over. Most apps quietly fudge this. Tot Up gives the odd penny to a person — the payer first, then people in the order they joined the trip — and writes it on the expense:

Sam pays £3.34; Priya and Amy pay £3.33 each.

The odd penny went to Sam.

Check it: £3.34 + £3.33 + £3.33 = £10.00, exactly. The shares of every expense always add up to its amount to the penny, and across the whole trip, everything everyone owes and is owed always adds up to exactly zero. Both of these are checked by the app on every single change — if a sum wouldn’t balance, the change is refused.

Foreign money: a dated, public rate — or your bank’s exact figure

Pay for dinner in euros and Tot Up converts it to pounds using the European Central Bank’s daily reference rate — a public, published number — for the day you paid. The expense shows its working, permanently:

€86.00 → £73.42 at the ECB rate for Fri 14 June 2026 (€1 = £0.8537)

Check it: 86.00 × 0.8537 = £73.42 (to the nearest penny). The ECB doesn’t publish rates at weekends or on European bank holidays, so a Saturday expense uses the most recent rate before it — and says so: “ECB rate for Fri 13 June (nearest to Sat 14 June)”. Once saved, the converted figure is frozen: it never drifts when rates move later.

Two honest caveats. First: your card was probably charged a slightly different amount — banks add their own margin. If the exact figure matters, type what your statement says and the expense will show “set by you” instead of the rate. Second: the ECB covers about thirty major currencies; for anything else, Tot Up asks for the pounds figure from your bank rather than inventing a rate. ECB reference rates are published for information — they’re our honest yardstick, not a promise about what your bank charged.

Written in pen, not pencil

Every trip is a ledger where nothing is ever overwritten. An edit doesn’t replace an expense — it adds a new version on top, and the old one stays in the history with a name and a date: “Ben changed the amount from €80 to €84.” A removed expense stays visible, crossed out, with one tap to put it back. Every balance on every screen is worked out fresh from that full history — so there is no secret running total that could quietly drift out of step with the facts. If the group ever disagrees about a number, you don’t argue — you look.

Settling up: fewer payments, fully explained

Suppose Ben owes Sam £30 and owes Amy £10, and Amy owes Sam £10. Tot Up can chain that together: Ben pays Sam £40, Amy pays nothing — one payment instead of three, and everyone ends up exactly where they should. That’s the “Fewer payments” mode, and because it can route money to someone who never spent on you directly, every line opens up to show precisely this kind of working. If you’d rather just pay back the people who actually paid for you, that mode is one tap away — same totals either way, to the penny. And a payment only moves the balances once both sides have confirmed it: the payer says “I’ve paid”, the payee says “Got it”.

Don’t trust us — check us

Any member can export the whole trip, free, any time: every expense, every version, every payment, with the original currency, the rate and its date. Open it in a spreadsheet and add it up yourself — it will match the app to the penny. An app that does its sums right has nothing to hide, so we hide nothing.