Percentage increase or decrease from A to B
Increase or decrease a number by a percent
Find the number before the change
About the percentage increase calculator
How much did a price, a rent or a score go up — in percent? Type the old number and the new number, and the calculator shows the percentage increase (or decrease) with the three steps: the change, divide by the old number, times 100.
Two more questions sit under it:
- Increase or decrease a number by a percent — 80 plus 25% is 100; 80 minus 25% is 60.
- Find the number before the change — after a 25% increase it is 100; what was it before? (80, not 75.)
Every answer updates as you type. Nothing is sent anywhere.
Features
- Percent change from A to B — an increase or a decrease (shown in red)
- Three clear steps — with your own numbers
- Swap — see how 80 → 100 (+25%) and 100 → 80 (−20%) differ
- Add or take off a percent — with the one-step multiplier
- Number before a change — the reverse percentage, with a check
- Multiplier shown — "new = old × 1.25"
- Decimals and negative numbers — 19.99 → 24.99, or −50 → −25
The percentage increase formula
Percentage change = (new − old) ÷ old × 100
- Find the change: new − old. From 80 to 100: 100 − 80 = 20.
- Divide by the old number: 20 ÷ 80 = 0.25.
- Times 100: 0.25 × 100 = 25% increase.
When the new number is smaller, the change is negative, so it is a decrease. From 100 to 80: (80 − 100) ÷ 100 × 100 = −20%.
| Example | Old | New | Change | Percent change |
|---|---|---|---|---|
| A price | 40 | 50 | +10 | +25% |
| Monthly rent | 1,200 | 1,260 | +60 | +5% |
| Town population | 2,500 | 2,800 | +300 | +12% |
| Test score | 60 | 72 | +12 | +20% |
| Train ticket | 80 | 60 | −20 | −25% |
| Phone bill | 250 | 200 | −50 | −20% |
| Shop price | 19.99 | 24.99 | +5 | +25.01% |
Increase or decrease a number by a percent
To add a percent, multiply by 1 + the percent ÷ 100. To take a percent off, multiply by 1 − the percent ÷ 100. Here is what happens to 80:
| Change | Multiply by | 80 becomes |
|---|---|---|
| +5% | 1.05 | 84 |
| +10% | 1.1 | 88 |
| +15% | 1.15 | 92 |
| +20% | 1.2 | 96 |
| +25% | 1.25 | 100 |
| +50% | 1.5 | 120 |
| +100% | 2 | 160 |
| −5% | 0.95 | 76 |
| −10% | 0.9 | 72 |
| −20% | 0.8 | 64 |
| −25% | 0.75 | 60 |
| −50% | 0.5 | 40 |
Find the number before the change
This is the reverse percentage. If a price is 120 after a 20% increase, the old price is not 120 − 20% (96). Divide by the multiplier instead: 120 ÷ 1.2 = 100. Check: 100 + 20% = 120.
After a decrease, divide by 1 − the percent ÷ 100. A coat costs 60 after 25% off: 60 ÷ 0.75 = 80.
Undo a change
A rise and a fall of the same percent do not cancel. Each one is taken from a different starting number. Up 25% from 80 gives 100; down 25% from 100 gives 75, not 80. To get back where you started:
| After going | You need to go |
|---|---|
| down 10% | up 11.11% |
| down 20% | up 25% |
| down 25% | up 33.33% |
| down 50% | up 100% |
| down 75% | up 300% |
| up 10% | down 9.09% |
| up 25% | down 20% |
| up 50% | down 33.33% |
| up 100% | down 50% |
Frequently asked questions
How do I calculate a percentage increase?
Take away the old number from the new one, divide by the old number and multiply by 100. From 50 to 65: (65 − 50) ÷ 50 × 100 = 30% increase.
How do I calculate a percentage decrease?
Use the same formula. The answer is negative: from 65 to 52, (52 − 65) ÷ 65 × 100 = −20%, so a 20% decrease.
What if the old number is 0?
Then there is no percentage change, because you cannot divide by 0. The calculator shows the change itself instead.
What if the numbers are negative?
The calculator divides by the size of the old number, so from −50 to −25 is a 25 increase, which is +50%.
How do I add 15% to a number?
Multiply by 1.15. For 200: 200 × 1.15 = 230. The second box does this and shows the steps.
Is a 100% increase the same as doubling?
Yes. A 100% increase adds the whole old number again, so 80 becomes 160. A 200% increase makes it three times as big.
Related tools
- Percentage Calculator — X% of Y, X is what percent of Y, and percent change
- Discount Calculator — the sale price after a percent off
- Sales Tax Calculator — add or remove tax from a price
- Inflation Calculator — what prices from the past are worth today
- Rule of Three Calculator — if A goes with B, what goes with C?
How to use it
- In the first box, type the old number (from) and the new number (to)
- Read the percent increase or decrease and the three steps
- Press Swap to turn the change around
- To add or take off a percent, use the second box
- To find the number before a change, use the third box
