Percentage Calculator: Increase, Decrease & Ratio Online
Percentage calculator online: calculate percentage increase, decrease, change, and ratios with step-by-step formulas for any numbers.
Updated 2026-08-16
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Features
- Calculate X% of a number (e.g., 20% of 150)
- Find what percent one number is of another
- Calculate percentage increase between two numbers
- Calculate percentage decrease between two numbers
- Calculate percentage change (increase or decrease)
- Instant calculation as you type
- Clear formula display showing the calculation
- Support for negative percentages
- Handles discount, tax, and statistics scenarios
How to Use
- 1Select the calculation type you need.
- 2Enter the first value (percentage or number).
- 3Enter the second value (number or percentage).
- 4View instant results with the formula.
- 5Switch between different calculation types as needed.
- 6Use 'Percentage of a Number' for calculating discounts or tips.
- 7Use 'Percentage Increase/Decrease' for analyzing price or salary changes.
- 8Use 'Percentage Change' for comparing before-and-after values in reports.
Frequently Asked Questions
How do I calculate X% of a number?
Multiply the number by the percentage divided by 100. For example, 20% of 150 = 150 × (20/100) = 150 × 0.2 = 30. This is useful for calculating discounts, taxes, or tips.
How do I find what percent one number is of another?
Divide the first number by the second, then multiply by 100. For example, to find what percent 30 is of 150: (30 / 150) × 100 = 20%. This shows that 30 is 20% of 150.
What's the difference between percentage increase and decrease?
Percentage increase measures how much a value grew: ((new - old) / old) × 100. Percentage decrease measures how much it shrunk: ((old - new) / old) × 100. Both use the original value as the base.
How do I calculate percentage change?
Use the formula: ((new value - old value) / old value) × 100. A positive result indicates an increase, negative indicates a decrease. For example, from 80 to 100: ((100-80)/80) × 100 = 25% increase.
Can percentages be greater than 100%?
Yes. Percentages over 100% mean the value is more than the whole. For example, if you had $100 and now have $250, that's a 150% increase. The new value is 250% of the original.
How do I calculate the percentage of my exam marks?
Divide the marks you obtained by the total marks, then multiply by 100. For example, 342 out of 400 is (342 / 400) × 100 = 85.5%. This works for school report cards, board exams (including SSLC/10th and 12th results), and college assignments. If you need an overall average across subjects, add up all obtained marks and all total marks first, then apply the same formula.
Why does my percentage calculator online result differ from Excel's?
Excel rarely disagrees with the math; it disagrees with the input. Formatting a cell as Percentage multiplies the displayed value by 100 while the underlying number stays a decimal, which causes off-by-100 mismatches; and entering 0.2 versus 20 in a formula gives completely different results. Also check cell rounding. The formula in this percentage calculator is the standard one, so compare the actual numbers you typed, not the formatted display.
How do I calculate a 20% tip on a restaurant bill?
Use the 'Percentage of a Number' mode. Enter 20 as the percentage and the bill amount as the number. For example, a $50 bill × 20% = $10 tip. Total = $60. Alternatively, you can calculate 10% ($5) and double it for the same result.
How do I calculate percentage profit or loss?
Use 'Percentage Change' mode. For profit: ((selling price - cost price) / cost price) × 100. For example, bought at $80, sold at $100: ((100-80)/80) × 100 = 25% profit. If selling at $60: ((60-80)/80) × 100 = -25% loss.
Why is a rate increase from 4% to 5% reported as both 25% and 1%?
Both numbers are correct; they measure different things. The absolute change is 1 percentage point (5% - 4%), and the relative change is 25% ((5-4)/4). News reports and rate comparisons mix the two on purpose, so always check which one is meant: absolute (percentage points) or relative (percent of the old rate). This calculator's increase/decrease mode gives you the relative figure; subtract the rates for the absolute one.
How do I calculate sales tax percentage?
Use 'Percentage of a Number' mode. Enter the tax rate as the percentage and the pre-tax amount as the number. For example, 8.5% of $50 = $4.25 tax. The total is $54.25. For reverse calculation (extracting tax from total), use the formula: (total / (1 + rate)) × rate.
Why can't I just average percentages to get a meaningful average?
Averaging percentages is only valid when every percentage applies to the same base. If one year grows 10% and the next 30%, the arithmetic mean (20%) is not the true average growth; you need the geometric mean computed from the actual values. The same trap affects survey percentages with different sample sizes. Use 'Percentage Change' mode with the real numbers instead of averaging the percentages.
What does a 100% increase actually mean?
A 100% increase means the value has doubled. If something goes from 50 to 100, that's a 100% increase because it increased by 50 (which is 100% of the original 50). A 200% increase means tripling (increase of 100 on top of 50 = 300% of original). This calculator helps avoid confusion between these common scenarios.
Why can't I just add percentages together?
Because each percentage is relative to its own base. A 50% increase followed by another 50% increase multiplies the value by 1.5 twice: 100 → 150 → 225, which is a 125% total increase, not 100%. The same applies to discounts: 20% off then 10% off is 28% total, not 30%. Always apply percentages sequentially to the running value, or let this calculator do it in the right order.
Why does my result differ from what I expected?
Three mistakes cause most mismatches: 1) Confusing 'what percent is A of B' with 'percent change': 20% of 150 is 30, but going from 150 to 180 is a 20% increase while going from 180 to 150 is a 16.7% decrease. 2) Using the wrong base: a price increase is relative to the old price, a discount to the original price. 3) Adding percentages directly (see the question above). Re-check which mode you selected and which number is the base.
Why does my smartphone calculator app give a different result than this percentage calculator?
Calculator apps disagree on what the % key does: most treat '50 + 10%' as 50 + (10% of 50) = 55, some evaluate it as 50 + 0.1 = 50.1, and others ignore it entirely. This tool uses explicit percentage math (X% of Y, percent change, increase/decrease), so enter the actual numbers instead of relying on a percent key, and the results will match the formulas.