How do I increase a number by a percentage?

Multiply by 1 plus the percentage divided by 100. Increasing 80 by 25% gives 80 × 1.25 = 100. A supplied 5% increase to 40,000 gives 42,000.

How do I subtract a percentage?

Enter a negative percentage. Starting at 100 with -20 gives 100 × 0.8 = 80. For a purchase discount constrained to 0–100%, use % off a price, which also reports the saving.

Do successive changes add up?

No. Apply each change to the latest result. A 25% increase from 80 gives 100; a later 25% decrease gives 75. For repeated compounding over a specified duration, use APY Calculator with the supplied rate and time convention.

Can a percentage be larger than 100 or apply to a negative number?

Yes, as numeric adjustment arithmetic. Adding 150% to 10 gives 25; subtracting 150% gives -5. Applying 25% to -80 gives -100 because the number is multiplied by 1.25. Those are stated numbers, not an automatically interpreted price or policy.

Add or Subtract a Percentage

Apply a percentage you already know to a starting number. This page starts with 80 and a 25% increase, producing 100. Enter -20 to reduce a number by 20%. Finding the percentage change between two known endpoints is a separate question; here the known rate determines the new value.

What is 80 after a 25% adjustment?100Increase the starting number by 25%.

Question

Starting number

Percentage to add or subtract

The working
80 × (1 + 25 ÷ 100)
Computed result
100
In words
Increase the starting number by 25%.

Change and difference are not the same thing. Going from 80 to 100 is a 25% increase, measured against where you started. But the percentage difference between 80 and 100 is 22.22%, because that one divides by the average of the two. Change has a direction; difference does not. Reports and spreadsheets mix these up constantly, which is why both are here as separate questions.

Margin and markup are the same profit over two different divisors. Something that costs 40 and sells for 100 earns 60 either way, but the margin divides that by the selling price and is 60%, while the markup divides it by the cost and is 150%. Margin can never pass 100%; markup has no ceiling. The profit margin question above reports both, each beside the number it divided by.

Common questions

How do I increase a number by a percentage?: Multiply by 1 plus the percentage divided by 100. Increasing 80 by 25% gives 80 × 1.25 = 100. A supplied 5% increase to 40,000 gives 42,000.
How do I subtract a percentage?: Enter a negative percentage. Starting at 100 with -20 gives 100 × 0.8 = 80. For a purchase discount constrained to 0–100%, use % off a price, which also reports the saving.
Do successive changes add up?: No. Apply each change to the latest result. A 25% increase from 80 gives 100; a later 25% decrease gives 75. For repeated compounding over a specified duration, use APY Calculator with the supplied rate and time convention.
Can a percentage be larger than 100 or apply to a negative number?: Yes, as numeric adjustment arithmetic. Adding 150% to 10 gives 25; subtracting 150% gives -5. Applying 25% to -80 gives -100 because the number is multiplied by 1.25. Those are stated numbers, not an automatically interpreted price or policy.

Browser double-precision arithmetic. Decimal results are rounded to twelve significant digits; safe integer results retain their full value. The formula shows the inputs used.