SplitWithUs

How the numbers are worked out

SplitWithUs settles a shared trip: who paid what, in which currency, and who should send how much to whom so that everyone ends up even. This page lists every rule the calculator applies, where its exchange rates come from, and what it deliberately does not do. If a number on your receipt looks wrong, the steps below are enough to check it by hand.

1. Where the exchange rates come from

We publish a snapshot of daily reference rates with the site, covering 154 currencies from Sep 27, 2024 to Sep 25, 2026. It is refreshed once a day. Your browser downloads only the currencies your trip uses, from this site; no third party sees what you enter.

  • Reference rates published by the European Central Bank are used wherever the ECB publishes one: AUD, BRL, CAD, CHF, CNY, CZK, DKK, EUR, GBP, HKD, HUF, IDR, ILS, INR, ISK, JPY, KRW, MXN, MYR, NOK, NZD, PHP, PLN, RON, SEK, SGD, THB, TRY, ZAR. These are the rates the ECB sets around 16:00 Central European Time on business days. We read them through the free Frankfurter service, which republishes them unchanged.
  • Every other currency comes from an open, daily market aggregate (the fawazahmed0 currency API). It is a market mid-rate, not a central bank figure, and it also covers weekends.

When both sources have a currency, the ECB figure wins on every day. A day-on-day jump of more than 20% is treated as bad data and left out. All rates are stored against the US dollar; a conversion from, say, yen to euros goes through that day's two dollar rates and is rounded once, at the end.

2. Which day's rate a receipt uses

  • The day it was paid. Not the day you settle up, and not today. A dinner on the 3rd uses the rate of the 3rd.
  • Weekends and holidays. Central banks do not publish then, so a receipt uses the last rate published before its date: a Saturday receipt uses Friday's rate. The receipt screen says so ("Sep 18 rate, the last published before Sep 19").
  • Older than the snapshot. We do not guess. Enter what your card actually charged instead, and that amount is used as it is.
  • What your card charged wins. If you enter the charged amount, the rate is not used for that receipt at all. This is the right choice when a card or an exchange booth used a worse rate than the reference rate.

Why the payment date and not the settle-up date: the guide on which exchange rate to use works through the difference.

3. Splitting a receipt

Each receipt is converted into the group currency once, then split evenly between the people who share it, in whole minor units: cents, pence, yen, won. There are never fractions of a cent. When the amount does not divide evenly, the leftover units go one each to the people sharing it, in list order (the order of names on step 1). So the parts always add back up to the receipt, exactly.

Example. $100.00 shared by three people: each part is $33.33 and one cent is left over. The first person on the list takes it: $33.34, $33.33, $33.33. Total $100.00.

Over a whole trip, this puts at most one extra minor unit per receipt on anyone. The proof page for every settlement shows who got each one.

4. From balances to transfers

Each person's balance is what they paid minus their part of everything they shared. Balances always add up to exactly zero; if they did not, the calculator would say so instead of hiding it. To turn balances into transfers, the person who owes the most pays the person who is owed the most, as much as possible, and this repeats until everyone is even. A group needs at most one fewer transfer than it has people. That is not always the absolute minimum possible, but it never changes what anyone owes, only the route the money takes. The guide on what "fewer transfers" does shows an example of each.

5. Home currencies

The group settles in one currency, so every total adds up to the cent. A friend who lives elsewhere can set a home currency; their amounts are then also shown in it, converted at the newest rate we hold (Sep 25, 2026). Those home-currency figures are approximate: the transfer itself is the group-currency amount, and your bank will use its own rate on the day you send it.

6. How to read the result

  • Balances. A plus means the group owes that person; a minus means they owe the group. Together they come to exactly zero.
  • Transfers. Each line is one payment from one person to another, in the group currency. Once every line is sent, every balance is zero.
  • The working. A shared settlement has a proof page that lists each receipt, the rate and date it used, and who carried each leftover cent. Read it top to bottom and you have redone the whole calculation.
  • Home-currency figures marked with "≈" are a guide only, as section 5 explains.
Example. Four friends: Ana paid $300 for the car, the rest paid nothing, and everyone shared it. Each part is $75.00, so Ana's balance is +$225.00 and the others are −$75.00 each. The result is three transfers of $75.00 to Ana. Nobody pays anyone else, because nobody else is owed.

These figures are a reference estimate for the group to agree on, not a statement of what anyone must pay; the disclaimer sets out what that covers. To run your own trip through these rules, open the trip calculator.

What this tool does not do

  • It does not know your bank's rate or fees. Reference rates are mid-market; banks, cards and exchange booths add a margin.
  • It does not move money, hold money or connect to any payment service. It tells you who should send what.
  • It does not give financial or tax advice.
  • It settles a trip after it ends. It is not a shared ledger several people edit at the same time.

Found a number you cannot reproduce with these rules? Write to us from the contact page with the receipt, and we will check it.