How the numbers are worked out

SplitWithUs settles a shared trip or a night out: 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 Nov 11, 2024 to Nov 10, 2026. It is refreshed once a day. Your browser downloads only the currencies your trip uses, from this site, so no rate provider sees which currencies or dates your trip has.

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, and so is a value more than 2.5 times away from the median of the last 90 published values, until a person has checked it. A share link keeps the day of the newest rate when it was made, so a rate published later does not change the amounts in it. 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 Central banks do not publish then, so a receipt uses the last rate published before its date: a Saturday receipt uses Friday's rate.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.

The guide on which exchange rate to use works through why the payment date is used and not the settle-up date.

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 (Nov 10, 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.

7. Restaurant and bar bills

The restaurant and bar bill splitter works in one currency for the whole night, so no exchange rate is involved. Each place is worked out on its own, in this order:

Items. Each item goes to the people who had it: everyone present, one person, a few people evenly, portions, a count (three of four beers) or an exact amount. Someone marked "pays only for their own items" is left out of shared dishes.
A treat. The items of a person who is treated are shared evenly by the others present at that place.
The extras, in order. The discount comes off first. A service charge is worked out on the discounted bill, tax on the discounted bill plus service, and the tip on either the discounted bill before tax or the total after tax, as you choose. Tax can also be none, or already included in the menu prices. Each percentage is rounded to the cent once.
Who carries the extras. Discount, service, tax and tip are shared in proportion to what each person had, or evenly per head if you choose.
One rounding. Each person's exact share of the whole bill is worked out first, and the bill is rounded once. Leftover cents go one at a time to the largest fractions of a cent, ties in list order, so the parts add up to the bill and an even split stays even.

Several places in one night are added up: each person's total owed minus what they paid gives their balance, and section 4 turns the balances into transfers.

Example. A $100.00 dinner shared by three, no tax, an 18% tip on the bill before tax: the tip is $18.00 and the bill $118.00. Each exact share is $39.333…, so rounding the bill once gives $39.34, $39.33 and $39.33. The first person on the list carries the leftover cent; the "Even split" tab says so rather than hiding it in a rounded-up figure.

The splitter does not look up tax rates or tipping customs. It guesses whether tax is added or included from the currency, and you enter the rate or the amount from the receipt.

8. Moving out

The move-out calculator works in one currency and settles three parts, each with its own rule, then adds them up per person and turns the balances into transfers as in section 4.

Final bills. Each bill covers a period, counting the first and last day. Each person's days lived in it run from their move-in day (or the start) to their move-out day (or the end). The bill is split in proportion to those days, or to room rent times days if you choose, so days a room stands empty fall to the people still there. Leftover cents go to the largest fractions, ties in list order. Each bill also shows its daily rate (the amount divided by the days it covers); for one person, that rate times their days is their prorated amount.
The deposit. Each person's part back is what they put in, less their deductions. A shared-space deduction is split evenly between everyone who put money in; a room's deduction is that person's. If the landlord refunds one person, that person sends each the rest of their part. If the lease goes on, whoever takes over pays each person moving out their part.
Shared stuff. Value now = price × (1 − whole months used ÷ months it lasts), rounded to the cent, and never below zero. An agreed value replaces it. Whoever keeps an item pays the other owners their equal shares of the value; a new roommate who buys in pays the value divided by the number of owners plus one; money from a sale is shared by the owners.

Example. A $90.00 bill for September 1 to 30; one roommate moved out on September 12. Days lived 30 : 30 : 12. Shares: $37.50, $37.50 and $15.00. A sofa bought for $900.00 and used 24 of its 60 months is worth $540.00.

A bill entered as an estimate can be given its real amount later. The first transfers stay as they were; the difference is split by the same rule and settled with a short top-up list.

9. A guest of honor

The guest of honor calculator is the trip calculator with one more rule, so sections 1 to 6 apply to it as they are.

Treated by kind. Each receipt has a kind. Restaurant, Cafe, Activity, Museum, Shop and Grocery start out treated; Hotel, Transport, eSIM and Other start out shared by everyone on the receipt. A single receipt can be switched either way.
Who carries a treat. On a treated receipt the guests of honor pay nothing, and the receipt is split evenly between the other people who shared it. Someone who was not on the receipt pays nothing toward it.
Several guests. Guests of honor never pay toward each other's treats. A treated receipt shared only by guests has nobody left to pay for it, so the calculator asks you to fix it before settling.
The comparison column. Next to each person's part, the result shows what it would be if all the guests' treated shares were added up and split evenly between everyone who is not a guest. The transfers follow rule 2, not the comparison.

10. A road trip

The road trip gas calculator works in one currency and splits fuel by leg, then tolls and parking, and turns the balances into transfers as in section 4.

Fuel for each leg. A leg's fuel comes from receipts or from one estimate, never both. An estimate is distance ÷ mpg × price per gallon, distance ÷ km/L × price per liter, or distance × L/100km ÷ 100 × price per liter, rounded to the cent once. A receipt with no leg picked is divided between the legs in proportion to their distances.
Driver relief. Each leg's fuel is split between the people on it by weight: 1 each when even; 1 for the driver and 2 for each rider for half a share; 0 for the driver and 1 for each rider when the driver skips fuel. A leg with no driver picked is split evenly. A leg where the driver skips fuel but rode alone is split evenly too, which puts its fuel on the driver.
Tolls and parking. Split evenly between the people each one was for, with no driver relief.
Leftover cents. Each leg's fuel, and each toll, is rounded on its own: leftover cents go to the largest fractions of a cent, ties in list order.

Example. 300 miles at 25 mpg, with fuel at $3.459 a gallon: 300 ÷ 25 = 12 gallons, × $3.459 = $41.508, rounded once to $41.51. With half a share and four people in the car, the driver counts 1 of 7 parts: $5.93, and each rider $11.86.

What happens to what you enter

This applies to all five calculators. The privacy policy lists the same points in full.

While you work. The calculation runs in your browser; names and amounts are not sent to our server. When a result is ready, the page adds one to a daily count of which tool was used, with nothing you entered in it.
On this device. A trip you are working on stays in its browser tab until you close it, and your last settlement stays on the device so you can reopen it. A night out, a move-out or a road trip stays on the device, so you can finish it later. Clearing your browser's site data removes it.
Only if you share. Pressing "Share to the group chat" stores the settlement on our server under a random ten-character id, with no IP address, cookie or account, and deletes it automatically 365 days later.
There is no account, and no email address or bank details are asked for.

What these tools do 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 expense list 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.