Percentage Increase & Decrease Calculator

Three ways to work with percentage change

Percentage change questions come in three flavours, and this calculator covers all of them. The first is percent change between two values: you know where you started and where you ended up and want the percentage. The formula is (new − old) ÷ |old| × 100, so a positive answer is an increase and a negative one is a decrease. Use it for price rises, salary changes, weight loss, traffic growth or any before-and-after comparison.

The second mode increases or decreases a number by a percentage. Enter a number and a percent and pick a direction to get the new value, for example 200 plus 15 % is 230 and 200 minus 15 % is 170. This is how sales prices, tax-inclusive prices and mark-ups are calculated: multiply by 1 + p ÷ 100 for an increase or 1 − p ÷ 100 for a decrease.

Working backwards to the original value

The third mode answers “what was it before?”. If a shirt costs 68 after a 15 % discount, the original price is 68 ÷ 0.85 = 80, not 68 plus 15 %. The percentage always refers to the original amount, so you divide rather than add back. The same idea reveals the pre-tax price of an item or the starting population before a known growth rate.

Common mistakes to avoid

Percent increases and decreases are not symmetric: a 50 % rise followed by a 50 % fall leaves you at 75 % of the start, not 100 %. Also keep percent change separate from percentage points. If an interest rate moves from 4 % to 5 %, that is one percentage point but a 25 % increase. The calculator prints the formula with your numbers so you can check every step and copy the working. If you are comparing two values with no clear “before” and “after”, the percent error calculator offers a symmetric percentage difference. All calculations happen in your browser and nothing is uploaded.