How to use the percentage increase calculator
- Type the starting number, such as a salary, price or bill.
- Enter the percentage and choose increase or decrease.
- Read the new figure and the amount added or removed.
How to increase a number by a percentage
Multiply by 1 plus the percentage as a decimal. A 4% pay rise on £28,000 is £28,000 x 1.04 = £29,120, so you gain £1,120 a year before tax. A 7% rent rise on £1,150 a month is £1,150 x 1.07 = £1,230.50, an extra £80.50 a month.
To decrease, multiply by 1 minus the percentage. Cutting a £2,400 budget by 15% gives £2,400 x 0.85 = £2,040, a saving of £360.
Why +10% then -10% does not get you back to the start
Each percentage works on whatever number is in front of it. Put £100 up by 10% and you have £110. Take 10% off £110 and you remove £11, leaving £99. The fall was worked out on a bigger number, so it took away more than the rise added.
The same happens the other way. A share that drops 50% needs to rise 100% to recover, because half of the original has to double to get back.
Several rises in a row also compound. Three yearly rises of 5% on £20,000 give £20,000 x 1.05 x 1.05 x 1.05 = £23,152.50, which is more than the £23,000 you get by adding 15% once.
Finding the original number before a rise
If a price is £60 after a 20% increase, the original was £60 / 1.2 = £50. Taking 20% off £60 would give £48, which is wrong for the same reason as the +10% and -10% example. Divide by the multiplier rather than subtracting the percentage. If you have two numbers and want to know the percentage between them, use the percentage change calculator instead.
Questions people ask
How do I add 10% to a number?
Multiply by 1.1. £450 plus 10% is £495.
How do I work out a 3% pay rise?
Multiply your salary by 1.03. On £32,500 that gives £33,475, a rise of £975 a year before tax and National Insurance.
How do I decrease a number by a percentage?
Multiply by 1 minus the percentage as a decimal. £80 less 25% is £80 x 0.75 = £60.
Is a 50% increase the same as multiplying by 1.5?
Yes. 1.5 is the original plus half again, so £40 increased by 50% is £60. A 100% increase doubles the number.