Which exchange rate to use when you settle a trip

Published September 27, 2026 by the developer of SplitWithUs (about)

After a trip abroad, every receipt has to be turned into one currency before anyone can say who owes what. The rate you use moves real money between friends, and people usually reach for one of three dates: the day the receipt was paid, the day you settle up, or the day the charge appears on the card statement. They do not give the same answer.

The three candidates

The payment date. The rate published for the day the money was spent. It reflects what the spending was worth when it happened, and it never changes afterwards, so the result is the same whether you settle the next day or next month.
The settle-up date. One rate, today's, for every receipt. It is simple, but if the currency has moved since the trip it shifts value between people: whoever paid in a currency that later fell gets back less than they spent.
The card statement. What the payer's bank actually took. For that one payer it is the most accurate figure there is, because it already includes the rate the card network used and any fee. But it only exists for card payments, and not everyone has it when the group wants to settle.

Why the settle-up date is the risky one

Example. Mia pays for a group dinner of ¥30,000 on 3 March. Suppose that day ¥150 buys one dollar: the dinner cost her $200.00. The group settles in May. Suppose by then ¥160 buys a dollar: at May's rate the same dinner is worth $187.50. Settling at May's rate, the group pays Mia back $12.50 less than the dinner cost her. Nobody did anything wrong; the difference came from the calendar.

The gap grows with the time between the trip and the settle-up, and with how far the currency moved in between. For a weekend away settled the following week it is often small. For a long trip settled at the end of the season it can be worth arguing about, and it lands on the people who paid the most, who are usually the ones who organised things.

What to use instead

By default, the rate for the day each receipt was paid. It is the only choice that does not depend on when you settle.
When the payer knows what their card charged, use that. It is what they are really out of pocket, fees included. A reference rate will be close to it but rarely identical, because banks and card networks add their own margin.
Weekends and holidays. Central banks publish reference rates on business days only. Use the last rate published before the payment date: a Saturday lunch takes Friday's rate.
Cash changed before the trip. The fair cost of that cash is what it cost the person who changed it. If they know it, use that figure rather than a reference rate.

Whichever you choose, choose it before the trip and write it down; the argument about rates only starts once someone notices that the currency moved. The guide on what to agree before a group trip has that and the other points worth settling in advance.

How the calculator handles it

SplitWithUs converts every receipt at the reference rate for the day it was paid, or the last one published before it. If the payer taps "Use what my card charged" and enters the amount from their statement, that amount is used instead and the rate is not applied to that receipt at all. The same field takes the cost of cash changed at a booth. The rate sources and the dates they cover are listed on the methodology page.

Limits

Reference rates are mid-market figures. They are a fair common yardstick, not the rate any bank gave you.
Foreign transaction fees and ATM fees are a separate question: are they part of the trip, or the cost of one person's choice of card? Agree it up front.
This is about being fair within a group of friends. It is not tax or accounting advice.