What is X% of Y?
Formula: (percentage ÷ 100) × number
Percentage Calculator
Find X% of a number, calculate percent change, add or subtract a percentage, or work backward to an unknown whole or original value.
Common Percentage Calculations
Calculate a percentage, compare a part with a whole, measure change, or adjust a known value.
X is what % of Y?
Formula: (part ÷ whole) × 100
Percentage Change
Formula: ((new value − old value) ÷ old value) × 100
Add a percentage (increase)
Formula: value × (1 + percentage ÷ 100)
Subtract a percentage (decrease)
Formula: value × (1 − percentage ÷ 100)
Reverse Percentage Calculations
Work backward to find an unknown whole or the original value before a percentage increase or decrease.
X is P% of what?
Formula: part ÷ (percentage ÷ 100)
The percentage cannot be zero.
Original value before a percentage increase
Formula: final value ÷ (1 + increase ÷ 100)
Use a percentage of zero or greater.
Original value before a percentage decrease
Formula: final value ÷ (1 − decrease ÷ 100)
Use a percentage from zero up to, but not including, 100.
Explore More Math Tools
Continue with related pages to compare results and improve decision making.
Percentage Calculations Available on This Page
This percentage calculator finds X% of a number, compares a part with a whole, measures percentage change, adds or subtracts a percentage, finds an unknown whole, and recovers an original value before an increase or decrease.
Core Percentage and Reverse Formulas
The core formula used by this percentage calculator is: Value = whole x (percentage / 100). Percentage = (part / whole) x 100. Whole = part / (percentage / 100). To reverse an increase, original = final / (1 + percentage / 100); to reverse a decrease, original = final / (1 - percentage / 100).
Each mode uses the value named in its formula as the base. Calculations retain full numeric precision; ordinary displayed answers use up to four decimal places, while very small nonzero answers use additional precision or scientific notation. A standard percentage change requires an old value above zero, and a 100% decrease has no unique reversible original.
If a value rose from 80,000 to 96,000, percentage change is 20%. If 96,000 is instead the final value after a known 20% increase, reverse mode recovers the original 80,000.
Percentage Calculation Examples
Find 15% of 200
(15 / 100) x 200 = 30.
15% of 200 is 30.
Add or subtract 20%
100 x (1 + 20 / 100) = 120. 100 x (1 - 20 / 100) = 80.
Adding 20% gives 120; subtracting 20% gives 80.
Find the unknown whole
60 / (30 / 100) = 60 / 0.30 = 200.
60 is 30% of 200.
Reverse a 20% increase
120 / (1 + 20 / 100) = 120 / 1.20 = 100.
The original value was 100.
Reverse a 20% decrease
80 / (1 - 20 / 100) = 80 / 0.80 = 100.
The original value was 100.
Choose the Right Percentage Mode
- Choose the card whose wording matches the value you need to find.
- Enter both known values using the same measurement or currency where applicable.
- Read the labeled result, formula, and substituted explanation; results update automatically.
- For a reverse decrease, enter a percentage from zero up to, but not including, 100.
When to Use the General Percentage Calculator
- Check add-percentage and subtract-percentage calculations against the correct base.
- Recover a whole when only a part and its percentage are known.
- Work backward from a changed value instead of incorrectly undoing it with the same percentage.
- Verify score, price, budget, and growth calculations with the formula shown beside each mode.
Focused Percentage and Price Tools
- Try the Add Percentage Calculator for a related calculation.
- Try the Discount and Tax Calculator for a related calculation.
- Read the Percentage Calculator Guide for examples and assumptions.
- Browse the Math Calculators page for more tools.
Related Calculators
Frequently Asked Questions
How do I find percentage of a number?
Multiply the number by the percentage and divide by 100, or use the calculator mode for instant results.
What is percentage change?
Percentage change measures how much a value moved relative to its original amount, expressed as a percent.
How do I add or subtract a percentage?
Multiply the starting value by 1 plus the percentage as a decimal to add it, or by 1 minus the percentage as a decimal to subtract it. Adding and then subtracting the same percentage does not usually return to the starting value because the base changes.
How do I reverse a percentage increase or decrease?
Divide the final value by 1 plus the increase rate, or by 1 minus the decrease rate. Use the reverse modes to recover the original value directly.
Why can a 100% decrease not be reversed?
A 100% decrease turns every starting value into zero, so the final zero does not identify one unique original value.