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Everyday Life · Five common modes

Percentage Calculator

Five percentage questions, one calculator. Pick what you’re trying to do, type the two numbers, and read the answer in a sentence.

Result

20% of 250 = 50

How we calculated your result

The five everyday percentage operations:

  • X% of Y = (X ÷ 100) × Y. Example: 20% of 250 = 50.
  • X is what % of Y = (X ÷ Y) × 100. Example: 25 of 200 = 12.5%.
  • % change from A to B = ((B − A) ÷ |A|) × 100. A positive result is an increase; negative is a decrease.
  • Add X% to Y = Y × (1 + X/100). Example: 200 + 15% = 230.
  • Subtract X% from Y = Y × (1 − X/100). Example: 200 − 15% = 170.

Official UK rules in simple English

There’s no “official” UK percentage rule, but a few conventions trip people up:

  • Percentage points vs percent. If a tax rate rises from 20% to 25%, that’s a 5 percentage-point increase but a 25% increase in the rate itself. Both framings are correct; choose deliberately.
  • Compound vs simple. Adding 10% and then 10% is +21%, not +20%. Use the compound interest calculator for repeated growth.
  • VAT. Adding 20% VAT to £100 gives £120. Removing 20% VAT from £120 gives £100, not £96. Use the VAT calculator if that’s what you’re actually trying to do.

Common pitfalls to watch out for

  • ⚠ A 10% drop followed by a 10% rise doesn't break even

    £100 down 10% = £90. £90 up 10% = £99 — not £100. You need a 11.1% gain to recover a 10% loss. This is why percentage drops in markets are worse than the headline suggests.

  • ⚠ Reversed direction matters

    If something costs £80 now and £100 last year, that’s a 20% decrease year-on-year. £100 to £80 is a 20% decrease; £80 to £100 is a 25% increase. The denominator is always the starting point.

  • ⚠ Adding 20% then taking 20% off ≠ original

    £100 + 20% = £120. £120 − 20% = £96. The percentages are taken from different bases, so they don’t cancel.

  • ⚠ Discount stacking isn't additive

    “30% off, then an extra 10% at the till” isn’t 40% off. £100 → £70 → £63 is a 37% total discount, not 40%.

Frequently asked questions

How do I work out a tip?
Use the ‘Add X% to Y’ mode. For a £60 bill with a 12.5% service charge: 60 + 12.5% = £67.50. In the UK, service is often already added to restaurant bills — check before tipping again.
How do I work out a discount?
Use ‘Subtract X% from Y.’ A £120 jacket at 30% off is 120 − 30% = £84. If you want to know the saving as a number, that’s the difference: £36.
What about percentages of percentages?
Use ‘X% of Y’ and put a percentage as Y. For example, 50% of 20% = 10%. Useful for partial pay rises (e.g. “I got half of a 4% rise” = 2%).

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