Tariq and Lena are on the sofa with a laptop between them and a half-eaten bowl of crisps wedged against the cushion. They’re made-up, but you may know them. They’re newly married, and they’ve picked twelve days in Mexico for the honeymoon. Flights are booked. Lena has opened a blank spreadsheet and typed “Budget” at the top in bold.
Then nothing. Neither of them knows what goes in the first row.
That blank page is the real obstacle in most trip budgets. The maths is easy; the structure isn’t. So here’s a structure you can copy, built around Tariq and Lena’s sofa session, with every number below made up for illustration.
Start with the currency you’ll be spending
Their instinct is to price everything in dollars, because that’s what their account says. It feels safe. It also means they’d have to convert every menu price in their head, and they’d guess.
Do it the other way round. Build the daily budget in pesos, since that’s the number on the menu, the bus ticket and the museum door. Do the conversion in one place, at the bottom, driven by one rate cell and nothing else.
Put the rate in, say, cell F1, with the date next to it. The USD to MXN page shows a current figure, refreshed hourly, so stamp the cell with the day you looked. For this example we’ll use an illustrative 18.00 pesos to the dollar. It’s a round number picked for easy sums, not a prediction.
Daily categories: the heart of the sheet
One line labelled “Spending money” is all Tariq wants. Lena says no. A lump hides the one thing that’s going to blow up. Split the day into a handful of categories and give each a daily figure in the local currency.
They settle on six. Lodging, food, local transport, activities, shopping and small extras, and tips. Each gets a number per day for the two of them together.
| Daily category | Pesos per day (illustrative) |
|---|---|
| Lodging | 1,800 |
| Food and drink | 1,100 |
| Local transport | 300 |
| Activities and entry fees | 600 |
| Shopping and small extras | 250 |
| Tips and small cash | 150 |
| Daily total | 4,200 |
Where do the numbers come from? Not from thin air. They come from looking at what things cost: nightly prices on the booking site, a few restaurant menus, a published bus fare, the entry price of the one ruin they most want to see. If a figure is a guess, mark it as one. Use a different colour for guesses and a plain colour for prices you’ve actually looked up, so you know which cells to firm up later.
Tips deserve their own row for a reason. Customs differ from country to country, and the money is easy to forget because it’s small and spread out. Check what’s normal where you’re going, then budget for it rather than being surprised at the table.
Multiply, then add what’s not daily
Twelve days at 4,200 pesos is 50,400 pesos. That’s the repeating part of the trip.
Now the one-offs, the things that happen once and wreck a daily average if you smear them across it. Tariq and Lena list two airport transfers at 600 pesos each, so 1,200, and a big day tour they’ve been eyeing at 2,400. That’s 3,600 pesos of one-offs.
Total in pesos: 50,400 plus 3,600 equals 54,000.
It helps to keep the one-offs in a separate block of the sheet, with a column for “paid already?” Flights and any prepaid hotel, if they went on a dollar card months ago, get a block of their own at face value. Only what’s still unpaid is exposed to the rate, so only that part goes through the steps below.
Convert once, in the right direction
Here’s the step where people flip the sum. With the rate stated as pesos per dollar, you go from pesos to dollars by dividing. 54,000 รท 18 = $3,000.00.
Check it with common sense: dollars are the bigger unit, so the dollar number should be smaller than the peso number. If your result is bigger, you multiplied. (Our MXN to USD page states the same relationship the other way round, as dollars per peso, where you’d multiply. Same truth, flipped. Just don’t mix the two.)
In the spreadsheet that’s one formula: the peso total divided by the rate cell, with the cell reference locked so it doesn’t drift when you copy it down. Change the rate and every dollar figure updates at once. That’s why the rate gets its own cell.
Add the cost of paying
A converted number isn’t what leaves the account. Using a card or a cash machine abroad can add fees, and they vary a lot from one provider to the next, so look up your own.
Some scale, as of November 2026. Capital One’s consumer guide calls a foreign transaction fee typically 1% to 3% of each purchase. Money.co.uk, a UK comparison site, says some UK cards charge 2.75% to 2.99% on non-sterling spending, and that cash withdrawals can draw a separate 2% to 3% cash-advance fee on top. Plenty of cards charge nothing at all, so your own terms are the only figures that count. Cash machines may also add an operator fee; the screen often shows it before you confirm.
Say Tariq and Lena plan to put 80% of spending on a card that charges 3%, and take 20% in cash. Illustrative maths: 80% of 54,000 is 43,200 pesos, which is $2,400 at 18. Three per cent of that is $72.00. Their subtotal becomes $3,072.00. If their card charges nothing, that row says zero, and the sheet still works.
Finish with a buffer, and test the rate
Last row: a buffer, as a percentage of the subtotal. They choose 10%, which adds $307.20 and brings the figure to $3,379.20. Not a magic number. It’s there for the daily guess that turned out wrong and for the rate.
Then do the cheap, useful thing. Change the rate cell to a worse number and watch. At an illustrative 17 pesos to the dollar, the same 54,000 pesos costs $3,176.47 instead of $3,000.00, a difference of $176.47 before fees. At 19, it costs $2,842.11, which is $157.89 less. They don’t need to guess which way it will go. They only need to see that their buffer comfortably covers the first case.
Or, put it as a short routine:
- Rate in its own dated cell.
- Six daily categories in local currency, times the number of days.
- One-offs in a separate block.
- Divide the local total by the rate once.
- Add fees, add a buffer, then try a worse rate.
Keep using it during the trip
The sheet doesn’t die when the plane leaves. Add a column called “actual” next to each category and fill it in each evening. By day four, Lena notices food is running at 1,500 a day against a plan of 1,100. It’s easy to fix on day four. It’s a nasty surprise on day twelve.
A caution about the rate cell: it’s a planning number. The card network and your issuer decide the real conversion, so the statement won’t match your sheet to the last digit. Official reference rates come with the same warning. The ECB labels its daily euro rates as information only and advises against transacting at them. Expect a small gap and let the buffer absorb it.
Up on his feet, stretching, Tariq finds the crisps are gone. Lena points at the screen. “Three thousand three hundred and seventy-nine,” she says, “and I know what’s in it.” That is the point of the whole exercise.
Sources
- Foreign transaction fees: What to know, Capital One
- Should you pay in local currency?, money.co.uk
- Euro foreign exchange reference rates, European Central Bank
Checked: November 2026
