Math tools
Free percentage calculator
Five focused modes — percent of, what percent, find the whole, percent change, and discount. Copy-ready results with optional CSV and PDF export.
What this percentage calculator does
A percentage is a number expressed as a fraction of 100 — one hundredth (1/100 or 0.01). The symbol % means “per hundred,” so 25% is the same as 0.25 or 25/100.
Most everyday questions fall into three patterns: How much is X% of Y? (percent of), What percent is X of Y? (share), and X is Y% of what? (find the whole). Pick the matching mode in the calculator above.
Percent of
Result = (P ÷ 100) × Base
How much is 20% of 50?
What percent
P = (Part ÷ Whole) × 100
Use the What percent mode
Find the whole
Whole = Part × 100 ÷ P
Use Find the whole mode
Quick example
20% of 50: (20 ÷ 100) × 50 = 10. The other way around: 10 is 20% of 50 (Find the whole mode).
Worked examples
- 20% of 70: 70 × 0.2 = 14 (Percent of mode)
- 15% of 200: 200 × 0.15 = 30
- What percent is 45 of 180? (45 ÷ 180) × 100 = 25%
- 50 is 25% of what? 50 × 100 ÷ 25 = 200 (Find the whole)
- Price drops from 100 to 80: percent change = −20%
Percentages appear everywhere — sale prices, exam scores, tips, profit margins, and labour-cost ratios. For shift scheduling and labour-cost scenarios, see ShiftOps or browse more free calculators.
Five modes compared
Each tab answers a different question. Choose the mode that matches your wording — not the formula you remember first. All five modes are included in one free percent calculator so you do not need separate tools for discounts or percent change.
| Mode | Question | Formula | Example |
|---|---|---|---|
| Percent of | How much is X% of Y? | Result = Base × P ÷ 100 | 20% of 50 = 10 |
| What percent | What share is the part? | P = Part ÷ Whole × 100 | 45 of 180 = 25% |
| Find the whole | X is Y% of what? | Whole = Part × 100 ÷ P | 50 is 25% of 200 |
| Percent change | How much did a value move? | ((New − Old) ÷ Old) × 100 | 100 → 80 = −20% |
| Discount | Price after a markdown? | Final = Base × (1 − P ÷ 100) | 100 − 20% = 80 |
How to calculate percentage increase or decrease
Percent change compares a new value to an original (old) value. The old value is always the base — a common mistake is swapping them. Use Percent change mode above, or follow these steps:
Find the difference
Subtract the old value from the new value: New − Old.
Divide by the old value
Divide the difference by the original amount (use the absolute value if the old value is negative).
Multiply by 100
Multiply by 100 to express the result as a percentage. A negative result means a decrease.
Example: price increase
Jeans rose from $36 to $45. Difference = 9. Then 9 ÷ 36 = 0.25, and 0.25 × 100 = 25% increase. In Discount mode, a 25% markdown on $45 gives a final price of $33.75.
Percentage formulas in Excel and Google Sheets
Use decimal equivalents (0.2 for 20%) or divide by 100 inside the formula. Format cells as Percentage when the result should display with a % sign. These formulas mirror the five calculator modes above.
| Task | Formula | Example |
|---|---|---|
| Percent of | =A1*(B1/100) | =50*(20/100) → 10 |
| What percent | =(A1/B1)*100 | =(45/180)*100 → 25 |
| Find the whole | =A1*100/B1 | =50*100/25 → 200 |
| Percent change | =((B1-A1)/A1)*100 | From A1 to B1 |
| Discount | =A1*(1-B1/100) | Price after B1% off |
Run a calculation above, then export as CSV (open in Excel or Sheets) or PDF with inputs, formula, and result.
Common percentage mistakes
Percentage points vs relative percent
A rate moving from 10% to 15% is a 5 percentage-point increase, but a 50% relative increase. Percent change mode uses the original value as the base.
Percent change vs percentage difference
This calculator offers percent change (old value as base). Symmetric percentage difference between two values uses a different formula and is not included here.
Rounding too early
Round at the end of a chain. Intermediate rounding often shifts totals in spreadsheets, invoices, and payroll reports.
Confusing part and whole
In What percent mode, the smaller share is usually the part and the total is the whole. Reversing them gives the wrong ratio — always check which number is the full amount.
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Frequently asked questions about this percentage calculator
How do you calculate a percentage of an amount?
Multiply the amount by the percentage divided by 100: Result = Amount × (P ÷ 100). Example: 15% of 200 = 200 × 0.15 = 30. Use Percent of mode above.
How much is 20% of 70?
20% of 70 = 70 × (20 ÷ 100) = 70 × 0.2 = 14. Enter base 70 and percentage 20 in Percent of mode.
How do you calculate percentage increase or decrease?
Use Percent change mode: ((New − Old) ÷ Old) × 100. Example: 100 to 125 → +25%; 100 to 80 → −20%. See the step-by-step section above.
How do you calculate a discount or sale price?
Choose Discount, enter the original price and discount percent. You get the discount amount and final price. Example: 100 with 15% off → discount 15, final 85.
What is the percentage formula?
Core patterns: Percent of = Base × P ÷ 100; What percent = Part ÷ Whole × 100; Find the whole = Part × 100 ÷ P. The mode table on this page maps each question to its formula.
How do you calculate percentage in Excel?
Typical formulas: =A1*(B1/100) for percent of, =(A1/B1)*100 for what percent, and =A1*(1-B1/100) for a discount. See the Excel section above for a full table.
What is the difference between percentage change and percentage difference?
Percent change compares a new value to an original baseline (included in this tool). Percentage difference compares two values symmetrically and is used in some scientific contexts — not in this calculator.
Can I export my calculation?
Yes. After each calculation you can download CSV or PDF with inputs, formula, and result — free, no account required.