Some of the most useful maths is the kind you do at the till, the restaurant or the petrol pump. A few simple calculations stop you from overpaying, help you split costs fairly, and let you spot when a 'deal' is nothing of the sort. This guide covers the everyday money skills everyone should have.
Tipping and splitting the bill
Working out a tip is just a percentage of the bill, and splitting it fairly means dividing the total — bill plus tip — by the number of people. A quick mental method: 10% is the bill with the decimal point moved one place left, so 15% is that figure plus half again. Tipping customs vary widely by country, from expected in some to unusual in others, so the right percentage depends on where you are. The tip calculator does the tip and the split at once, ending the awkward maths at the end of a meal.
Adding sales tax
When a price is quoted before tax, the final cost is the amount plus the tax rate applied to it — multiply by 1.18 to add 18%, for instance. In many countries the displayed price already includes tax, while in others it is added at the till, which catches out travellers. The sales tax calculator adds it instantly, and for value-added tax the VAT calculator can both add it to a net price and remove it from an inclusive total.
Removing tax from a total
Going the other way — finding the pre-tax price inside an inclusive total — trips many people up, because you cannot simply subtract the percentage. Instead, divide by one plus the rate: a 1,180 total that includes 18% tax came from 1,180 ÷ 1.18 = 1,000, with 180 of tax. This 'reverse' calculation matters for expense claims and for businesses recording the tax portion separately, and it is exactly where hand calculations go wrong.
Is that discount real?
Shops love a big percentage off, but the real saving is what you actually pay. The discount calculator turns a percentage off into the final price and the money saved, so you can judge whether a deal is as good as it looks. Watch for the order of operations too: a discount applied before tax leaves you paying tax on the lower price, while 'stacked' discounts (an extra 10% off an already reduced price) do not simply add up — 50% off then 10% off is a 55% saving, not 60%.
Compare like with like
The cheapest pack on the shelf is not always the best value. Converting every option to a price per unit — per 100 grams, per litre, per item — reveals the real bargain, because bigger packs are not always cheaper per unit, and clever packaging often hides this. Supermarket shelf labels show unit prices for exactly this reason, but they are easy to miss, and the units sometimes differ between brands. The unit price calculator makes the comparison instant and honest.
Estimating your bills
Knowing what an appliance costs to run helps you budget and cut waste. The cost depends on the appliance's power in kilowatts, how many hours it runs, and your electricity tariff per unit (kWh). For example, a 1,000-watt heater (1 kW) used 5 hours a day for 30 days uses 150 kWh; at a tariff of, say, 8 per unit that is 1,200 a month — often a surprise that changes how people use it. The electricity bill calculator turns an abstract tariff into a real, monthly number you can act on.
Money on the move: currency and travel
Everyday money maths follows you abroad, where a couple of habits prevent overpaying. Exchange rates always come with a margin, and the headline 'no-fee' booths often hide a poor rate, so compare the rate you actually receive, not just the advertised fee. A quick way to sanity-check prices is to memorise one round conversion — if a currency is roughly 90 to your own, then 900 is about 10 — so you can judge whether something is dear or cheap on the spot. When paying by card abroad, always choose to be charged in the local currency rather than your home one, as the 'convert for me' option usually applies a worse rate. The same instinct that makes you check a unit price at home protects your wallet on holiday.
Small habits, real savings
None of these calculations is difficult, but using them consistently is what saves money. The habits that add up are: tipping and splitting fairly without stress, knowing whether a price includes tax, checking the unit price rather than the headline price, treating flashy discounts with healthy scepticism, and understanding which appliances drive your bills. Each is small on its own, but together they put you firmly in control of your everyday spending — and the calculators here do the arithmetic so the only effort required is the habit of pausing to check.