Less than you think. That’s the answer for most trips, and it’s worth saying first because the usual mistake goes the other way: a thick envelope of notes bought at a bad rate, half of it brought home again.
Here’s how to find your own number in about five minutes.
Start from what only cash can buy
Forget the total trip budget. Cash only needs to cover what a card can’t. Write down the things on your trip that are likely to be cash-only:
- Taxis from the airport, and small local transport.
- Markets, street food, tips, public toilets, tolls.
- Small guesthouses and family-run places that don’t take cards.
- Anywhere the card terminal is “broken today”.
Put a rough daily figure next to that list. Ask your hotel, or look for recent traveller reports, and keep the number rough. That’s your cash-only spend per day.
Everything else goes on the card, in the local currency. The separate piece on DCC explains why that last phrase matters.
The formula
Here’s the rule. Cash to take from home = arrival costs + two days of cash-only spend + a buffer of around 20%. Everything after that comes from an ATM at the destination.
Why only two days? Because the first things you’ll need are the taxi and a meal, and by day three you’ve found a bank ATM in daylight with your jet lag gone. Why not more? Because every extra note is bought at a retail rate, carried, and either spent or brought home.
When to bring more
Raise the number when the trip is short and cash-heavy, when you’re heading somewhere remote where machines run dry or sit far apart, or when you’re arriving late at night or at a weekend and need a taxi, a room deposit and breakfast before any bank opens. Also bring more if your card has a low daily limit and you know a big cash payment is coming, such as a deposit for a rental.
When to bring less
Lower it when you’re visiting a large city where cards are taken nearly everywhere, when your card has no foreign fees, and when the trip is short enough that the cash-only list is tiny. Plenty of travellers can land with the price of a taxi and a coffee, and nothing else.
Which currency
Bring the currency of the country you land in, not a third one. Changing dollars into a different currency at the destination means two conversions, each with its own gap, so you pay twice. If you pass through another country on the way, a small float of that country’s money for a coffee isn’t worth buying in advance. Pay that by card.
Small notes
Ask for a mix of denominations when you order. A pile of large notes is awkward when the stall owner can’t give change. That said, a few more notes is a convenience, not a reason to bring extra total value.
Worked example
Take a made-up traveller called Dana, on a seven-day city break. Dana’s hotel and most restaurants take cards. These numbers are illustrative.
| Item | Amount (illustrative) |
|---|---|
| Taxi from airport | $30 |
| Cash-only spend per day | $25 |
| Two days of that | $50 |
| Subtotal | $80 |
| 20% buffer | $16 |
| Cash to bring from home | $96, call it $100 |
The full week of cash-only spending would be 7 × $25 = $175. Dana brings $100 and takes the other $75 or so from an ATM when needed. If the machine charges a flat fee, one withdrawal covers it. Fewer trips to the machine means fewer fees, as the guide to getting cash abroad explains.
Now a different trip. Say ten days somewhere where cards are patchy and you expect to spend $70 a day in cash. That’s $700 in total. Bringing everything would be a lot of cash to carry, so you might bring a few days’ worth, $210, and plan two ATM stops. If you can’t be sure ATMs are available at your destination, ask a recent traveller or your accommodation before you go, and carry more. Judgement, not a formula, is what’s left after that.
Check the rate first
Before you buy any foreign cash, check what it costs against the market rate. A page such as USD to MXN shows the benchmark, and rates are refreshed hourly. Compare it with the rate on the quote from your bank or exchange provider. A large gap on a small amount is annoying. On a large amount, it’s real money. Our airport exchange guide has the numbers on how wide that gap can get.
Limits that cap your number
Insurance
Which? advises carrying only as much cash as your travel insurance covers, in case it’s lost or stolen. Policies often set a single-item or cash limit, but the limit varies by insurer and policy, so read yours. If the cash limit is a few hundred in your currency, that’s a sensible ceiling.
Customs declaration thresholds
Every country has its own rules. The table below draws only on official pages, as of November 2026. Check the rules of your destination, and of anywhere you transit, before you travel.
| Region | Rule, as published |
|---|---|
| United States | No cap on carrying money in or out, but amounts over $10,000 must be reported to CBP on FinCEN Form 105 |
| Great Britain | Declare cash of £10,000 or more (or equivalent) when travelling to or from a country outside the UK; group totals count |
| Northern Ireland | Declare €10,000 or more (or equivalent) when travelling to or from a non-EU country, and when arriving from Great Britain |
| European Union | Declare cash of €10,000 or more (or equivalent) when entering or leaving the EU |
“Cash” can include more than banknotes: travellers’ cheques and other bearer instruments count in these rules. Customs in the EU can act on smaller amounts if they suspect criminal activity, and some EU countries have their own rules for cash moved between EU countries.
The UK page says undeclared cash can be seized and getting it back may involve a penalty. That is a bad way to spend a holiday. If your trip is anywhere near a threshold, declare it. Many other countries set their own, often lower, limits, and some restrict taking local currency in or out at all. This isn’t legal advice, so check with the border authority of each country you will pass through.
Where to keep it
Don’t keep all of it in one place. A little in your pocket for the day, the rest in the hotel safe or a locked bag. A second card in a different spot from the first. Fold a small note into a separate pocket for the taxi home.
Don’t flash a thick wallet at a market stall. Count notes away from the counter.
What if you end up with leftovers?
You will, sometimes. Spend it on the last day: a good meal, souvenirs, the airport coffee. Anything you can’t spend, keep for next time if you’ll go back to that country. Selling it back at an exchange desk usually costs a second spread, since desks quote a buying rate and a selling rate, and the gap shows up in whichever direction you go.
That’s also a reason to bring a bit less in the first place.
The shortlist
- Work out the cash-only spend per day.
- Bring arrival costs plus two days, plus about 20%.
- Get the rest from a bank ATM at the destination, in local currency.
- Keep it under your insurance cash limit and well under any declaration threshold.
- Split it across two places.
To compare several destination currencies against yours, the rate grid is a quick benchmark.
Sources
- Money: know before you go (U.S. Customs and Border Protection)
- Take cash in and out of the UK (GOV.UK)
- EU cash controls (European Commission)
- Spending abroad: the 4 dos and 5 don’ts (Which?)
Checked: November 2026
