The pound isn't what it used to be. In fact if you're traveling to Europe this summer, it's about two thirds of what it used to be! So it's not our fault that we're going to be getting through a bit more holiday spending money that in recent years. Or is it?

A recent survey shows it's not the exchange rate leading us astray, that's just our best excuse.

The survey, by American Express Global Foreign Exchange Services, listed the top five reasons for blowing the holiday budget as:

1. I like to treat myself when abroad (51%)

2. I get confused with the conversion of rate when spending abroad (46%)

3. I find things cost more than I expect them to (17%)

4. I don't realise how much I am spending (8%)

5. I cannot relate the foreign currency to real money, I tend to treat the money as monopoly money (6%)

Four of the five come down to one basic point. We're rubbish at currency maths.

It didn't seem important when it was all about calculating angles and the area under a curve, but now bad maths is costing us £975 million a year on holiday – which is about £15 per person per trip.

So, before you go, visit a site like XE, and work out how many pence your chosen currency is worth. Then write it down so you don't forget. So, for example, one Turkish lira is worth almost 39p.

Then when you're out and about take a calculator and do your sums. That cup of coffee for 5 lira, that's 5x39, or 195p (£1.95).

If you don't want to be faffing around with a calculator, and your mental arithmetic is OK, just get stuck into a bit of rounding, so that lira is worth about 40p. So five lira is 5x40, that's 200p (£2) ish.

And if your maths really is hopeless, do the sums before you go. Get out a piece of paper, and get the website to calculate, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40 and 50 of that currency and make a note of it. Then you'll know roughly what everything costs.

Of course, there's no cure for wanting to treat yourself when you're away, so these cunning solutions mean more than half of us will be blowing the budget anyway... but at least we'll be aware when we're doing it.