Three common percentage questions
The starting number matters. For an increase or decrease, the original value is the baseline. Using the new value as the denominator answers a different question.
- What is 15% of 200? Multiply 200 by 0.15 to get 30.
- 200 increased to 230 is what percentage increase? Divide the change, 30, by the original 200: 15%.
- What percentage is 30 of 200? Divide 30 by 200: 15%.
The percentage-change formula
Percentage change is (new value minus original value) divided by original value, multiplied by 100. A positive result means the value increased. A negative result means it decreased.
If a price changes from 80 to 100, the change is 20. Divide 20 by 80 and multiply by 100: the increase is 25%. If the same price moves from 100 down to 80, the decrease is 20%, because the original baseline is now 100.
Where people commonly make mistakes
- Using the new value instead of the original value as the baseline.
- Confusing percentage points with percentage change.
- Mixing prices that include tax with prices that exclude tax.
- Rounding each intermediate step before the final answer.
Check the result before using it
Use the calculator to compare a written calculation, a discount, a business metric or a change over time. For financial, tax or reporting decisions, keep the original figures and note whether they are gross, net, tax-inclusive or tax-exclusive.
Common questions
What is the percentage increase from 80 to 100?
The increase is 25% because the change of 20 is divided by the original 80.
What is the difference between percentage points and percent?
A move from 40% to 50% is a 10 percentage-point increase, but it is a 25% relative increase from the original 40%.
Can I calculate a discount with this tool?
Yes, but make sure you distinguish the discount amount from the final price after the discount.