Four quick percentage calculators on one page: a percentage of a number, what percent one number is of another, the percentage change between two numbers, and adding or taking off a percentage.
"Percent" means "out of a hundred". Every percentage question is one of these four:
number × X ÷ 100. 15% of 240 = 240 × 15 ÷ 100 = 36.
A ÷ B × 100. You saved 450 of a 600 goal: 450 ÷ 600 × 100 = 75%.
(new − old) ÷ old × 100. Rent goes from 800 to 860: 60 ÷ 800 × 100 = 7.5% more.
number × (1 + X ÷ 100) to add, number × (1 − X ÷ 100) to take off. 250 + 8% = 270; 250 − 8% = 230.
A common mistake: if a price of 110 already includes 10% tax, the price without tax is not 99 (110 − 10%). Divide instead: 110 ÷ 1.10 = 100. The tax is the 10 in between.
When an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25 percent (1 ÷ 4 × 100). News and banks use both, so it is worth knowing which one you are reading.
Multiply the number by the percentage and divide by 100. 15% of 240 is 240 × 15 ÷ 100 = 36.
Divide the part by the whole and multiply by 100. 45 out of 60 is 45 ÷ 60 × 100 = 75%.
Take the new value minus the old value, divide by the old value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% more.
Because the fall is taken from the bigger number. 100 + 20% = 120, then 120 − 20% = 96. Percentages always work on the number they start from.
A calculator gives you one answer. A cashbook shows you the whole picture: write down cash in and cash out, see where the money goes in charts and on a calendar, and share a ledger with your family, team or friends.
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