Percentage Calculator

When this calculator helps

Percentages turn up constantly in everyday British life, and this page bundles the five most common jobs into one tool. Reach for it when a shop window says 30% off and you want the actual price, when your salary review quotes a 4% rise and you want it in pounds, or when you are splitting a restaurant bill and a 12.5% service charge has already been added. Each tab answers one type of question, so you pick the one that matches what you are trying to find.

The core jobs are: working out X% of a number (20% of £150), finding what percentage one number is of another (£30 out of £150 is 20%), and measuring a percentage increase, decrease or change between two figures. Between them they cover discounts in the sales, mark-ups on a cost price, exam marks expressed as a percentage, and pay rises — the percentage questions that come up week to week rather than once a year.

How to read your result

Each mode gives a slightly different kind of answer, so it helps to know what you are looking at. The percent-of tab returns a plain amount — 20% of £150 is £30. The what-percentage tab returns a proportion — £30 of £150 is 20%. The change tab returns a signed figure: a move from £100 to £150 is +50%, and from £100 to £50 is −50%, with the sign telling you whether it went up or down.

The trap worth flagging is the difference between a percentage and a percentage point. If a savings rate moves from 5% to 8%, that is a rise of 3 percentage points, but a 60% relative increase. Both descriptions are correct; they answer different questions. This calculator's change tab always works in relative terms, so feed in 5 and 8 and you will get +60%, not +3.

A worked example

Imagine a coat priced at £150 in a 30% sale. Put £150 in the value box and 30 in the percent box on the Add/Subtract tab, choose subtract, and you get £105, with the £45 saving shown alongside. Now suppose the till receipt only shows the £105 sale price and you want to check the original: switch to Reverse %, enter £105 as 70% of the original, and it returns £150.

For a pay example, say you earn £32,000 and are offered a 4% rise. The percent-of tab turns 4% of £32,000 into £1,280, so the new salary is £33,280. If instead you knew the old and new figures and wanted the percentage, the change tab would take £32,000 to £33,280 and return +4%.

Common mistakes to avoid

Most percentage errors come from mixing up the base you are working from or confusing relative and absolute change.

• Confusing a percentage change with percentage points — going from 5% to 8% is +3 points but +60% in relative terms.
• Trying to reverse a 20% increase by subtracting 20% — £100 plus 20% is £120, but £120 minus 20% is £96, not £100. To undo it you divide by 1.20.
• Calculating a percentage of the wrong base — a discount comes off the original price, while a mark-up is added to the cost price.
• Forgetting that two successive percentage changes do not simply add — a 10% rise then a 10% fall leaves you below where you started.

Everyday UK percentage uses

The single most common percentage in British life is VAT at the standard 20% rate, applied to most goods and services. Use the Add/Subtract tab to add 20% to a net price, or Reverse % to strip VAT out of a gross total (divide by 1.20). Some items sit at the reduced 5% rate or are zero-rated, so check the rate before assuming 20%.

Beyond VAT, percentages run through tipping and the optional service charge of around 10 to 12.5% that appears on many restaurant bills, exam and coursework marks expressed as a percentage, mortgage and savings interest rates, and the discounts that drive seasonal sales. Whenever a figure is described 'per cent', one of the five tabs above will turn it into the pounds-and-pence answer you actually need.