Percentage calculator

Q: Which mode do I use for discounts?

Use Change mode with a negative percentage for discounts. Example: Original $100, 25% off → enter 100, -25% → result $75. Or use Percent of to find just the discount amount (25% of 100 = $25).

Q: How do I find the original price before a sale?

Use Reverse mode. Enter the sale price and the discount percentage (as negative). Example: Paid $80 after 20% off → enter 80, -20% → original was $100.

Q: What's the difference between Difference and Change modes?

• Change mode: you know the percentage, want the result (100 + 20% = 120) • Difference mode: you know two values, want the percentage (80 → 100 = +25%)

Q: Why does my result show so many decimal places?

Adjust the Decimal places setting in the bottom bar. Default is 2. Set to 0 for whole numbers, or up to 6 for high precision.

Q: Can I calculate compound percentages?

Do them in steps. For 10% then 5% increase: First calculate 100 + 10% = 110, then calculate 110 + 5% = 115.50. *Note: This is NOT the same as 15% increase (which would be 115).*

Q: Why is finding the original tricky?

Because percentages are relative. After 20% off, you paid 80% of original. So $80 ÷ 0.80 = $100 original. Simply adding 20% back ($80 + 20% = $96) gives wrong answer because you're adding 20% of the reduced price, not the original.

Q: How accurate are the calculations?

The calculator is mathematically precise. Results are displayed rounded to your chosen decimal places, but internal calculations use full precision.

Q: Do I enter 15 or 0.15 for 15%?

Enter 15 for 15%. The calculator treats the percentage field as a percentage, not a decimal. It handles the division by 100 internally.

5 calculation modes for all your percentage needs

12 min read Beginner Updated Feb 6, 2026

Overview

The Percentage Calculator handles all your percentage math needs with 5 specialized calculation modes. Whether you need to calculate a discount, find percentage change, or reverse-engineer an original price, this tool makes it instant and easy.

5 modes

Percent of, Change, What percent, Difference, Reverse

Auto-calculate

Results update as you type

Formula display

See the math behind results

Copy results

One-click copy for result and formula

Interface overview

The Percentage Calculator has a clean layout with mode selection at the top, input fields on the left, and results on the right.

Calculation mode section

At the top, you see 5 mode buttons in a row. The active mode is visually highlighted. Click any button to switch modes. The section can be collapsed with the arrow icon on the right.

Input values section (left)

The left panel contains input fields that change based on the selected mode. Each mode has different fields like Percentage (%), Number, Original, New, etc. A trash icon clears all inputs.

CALCULATE button

The orange CALCULATE button sits between input and result areas. Click it to calculate (or enable Auto-calculate for instant results).

Result section (right)

The right panel shows your result with a large number display and a FORMULA section below showing the calculation. Both have copy buttons.

Bottom settings bar

At the bottom: Auto-calculate toggle, Decimal places selector, CALCULATIONS counter, LAST RESULT display, and current MODE indicator.

Percentage calculator interface overview

Complete interface with mode selection, input fields, results, and settings bar

5 Calculation modes

The Percentage Calculator offers 5 specialized modes, each designed for a specific type of percentage calculation. Click any mode button to switch:
• Percent of: Find X% of a number (X% of Y)
• Change: Calculate percentage increase or decrease
• What percent: Find what percentage X is of Y
• Difference: Calculate % difference between two values
• Reverse: Find the original value before a % change

Each mode changes the input fields to match what that calculation needs.

Percent of mode X% of Y

The most common percentage calculation. Find what a percentage of a number equals.

Select Percent of mode

Click the Percent of button (shows "X% of Y" below it). It's usually the first/default mode.

Enter the percentage

In the Percentage (%) field, enter the percentage as a number. For 15%, type 15 (not 0.15). Placeholder shows "e.g., 20".

Enter the number

In the Number field, enter the value you want to find a percentage of. Placeholder shows "e.g., 80".

View the result

The result shows immediately.
Example: 20% of 80 = 16.
The FORMULA section shows: 20% × 80 = 16.

Calculating 20% of 80 with result and formula display

Common uses

Tips: 15% of $50 = $7.50
Tax: 8% of $100 = $8
Discounts: 25% of $80 = $20 savings

Change mode % Increase/Decrease

Calculate the result after a percentage increase or decrease. Perfect for price changes, tax additions, and discounts.

Select Change mode

Click the Change button (shows % Increase/Decrease below it).

Enter the starting value

In the Number or Original value field, enter your starting amount. This is the "before" value.

Enter the percentage change

In the Percentage (%) field, enter the increase or decrease percentage. Use positive for increase, negative for decrease (or there may be separate +/- toggle).

View the new value

Result shows the value after the change.
Example: 100 increased by 25% = 125.
Formula: 100 × 1.25 = 125.

Calculating percentage increase or decrease

Increase vs Decrease

Increase: 100 + 20% = 120 (multiply by 1.20)
Decrease: 100 - 20% = 80 (multiply by 0.80)

What percent mode X is Y% of Z

Find what percentage one number is of another. Great for test scores, proportions, and comparisons.

Select What percent mode

Click the What percent button (shows "X is Y% of Z" below it).

Enter the part (X)

In the first field, enter the smaller number or the "part". This is what you want to express as a percentage.

Enter the whole (Z)

In the second field, enter the larger number or the "whole". This is the total or base value.

View the percentage

Result shows the percentage.
Example: 42 is 84% of 50.
Formula: (42 ÷ 50) × 100 = 84%.

Finding what percentage one number is of another

Common uses

Test scores: 42/50 = 84%
Savings rate: $300 saved of $2000 income = 15%
Completion: 75/100 tasks = 75%

Difference mode % Between values

Calculate the percentage difference or change between two values. Useful for comparing prices, tracking growth, or measuring change over time.

Select Difference mode

Click the Difference button (shows % Between values below it).

Enter the original value

In the Original or From field, enter the starting/old value. This is your reference point.

Enter the new value

In the New or To field, enter the ending/new value. This is what you're comparing to.

View the % difference

Result shows the percentage change.
Example: From 80 to 100 = +25% increase.
Formula: ((100 - 80) ÷ 80) × 100 = 25%.

Calculating percentage difference between two values

Positive vs Negative

Positive % = increase (new > old)
Negative % = decrease (new < old)
Example: 100 to 75 = -25%

Reverse mode Find original

Find the original value before a percentage change was applied. Perfect for figuring out pre-discount prices or original amounts.

Select Reverse mode

Click the Reverse button (shows Find original below it).

Enter the final value

In the Final value or After field, enter the value after the percentage change. This is what you have now.

Enter the percentage change

In the Percentage (%) field, enter the percentage that was applied. Use negative for discounts, positive for increases.

View the original

Result shows the original value.
Example: $80 after 20% off → Original was $100.
Formula: 80 ÷ 0.80 = 100.

Finding the original value before percentage change

Common mistake

Don't just add the percentage back! $80 + 20% = $96, NOT $100. The reverse formula accounts for the fact that 20% off means you paid 80% of original.

Result & formula display

The result section shows your answer and the mathematical formula used:

Result display

Large number showing the calculation result. Before calculating, shows -- with message Enter values to calculate.

Copy result button

Click the copy icon next to the result to copy just the number to your clipboard.

FORMULA section

Shows the mathematical formula used. Example: "20% × 80 = 16" or "(42 ÷ 50) × 100 = 84%". Helps you understand the calculation.

Copy formula button

Click the copy icon next to the formula to copy the entire formula string.

Settings & statistics bar

The bottom bar provides settings and tracks your calculation history.

Auto-calculate toggle

When checked (default), results update instantly as you type. When unchecked, you must click CALCULATE button manually.

Decimal places selector

Choose how many decimal places to show in results. Default is 2. Options range from 0 to 10. Affects display precision.

CALCULATIONS counter

Shows total number of calculations performed in this session.
Example: "67 CALCULATIONS". Resets when you close the tool.

LAST RESULT display

Shows your most recent calculation result for quick reference. Shows "--" if no calculations yet.

MODE indicator

Orange badge showing current active mode. Example: "Percent of MODE". Quick visual confirmation of which calculation type is selected.

Bottom bar with auto-calculate, decimal places, calculations counter, and mode indicator

Practical examples

Sale discount

Item is $80, 25% off.
Change mode: 80 decreased by 25% = $60. You pay $60, save $20.

Restaurant tip

Bill is $45, want 18% tip.
Percent of mode: 18% of 45 = $8.10.
Total with tip: $53.10.

Test score

Got 42 out of 50 correct.
What percent mode: 42 is what % of 50 = 84%.

Price increase

Gas was $3.20, now $4.00.
Difference mode: from 3.20 to 4.00 = +25% increase.

Original price

Paid $120 after 20% off.
Reverse mode: What was original? = $150.

Add tax

Price $50, tax 8%.
Change mode: 50 increased by 8% = $54 total.

Frequently asked questions

Use Change mode with a negative percentage for discounts.
Example: Original $100, 25% off → enter 100, -25% → result $75.
Or use Percent of to find just the discount amount (25% of 100 = $25).

Use Reverse mode. Enter the sale price and the discount percentage (as negative).
Example: Paid $80 after 20% off → enter 80, -20% → original was $100.

• Change mode: you know the percentage, want the result (100 + 20% = 120)
• Difference mode: you know two values, want the percentage (80 → 100 = +25%)

Adjust the Decimal places setting in the bottom bar. Default is 2. Set to 0 for whole numbers, or up to 6 for high precision.

Do them in steps. For 10% then 5% increase: First calculate 100 + 10% = 110, then calculate 110 + 5% = 115.50.
Note: This is NOT the same as 15% increase (which would be 115).

Because percentages are relative. After 20% off, you paid 80% of original. So $80 ÷ 0.80 = $100 original. Simply adding 20% back ($80 + 20% = $96) gives wrong answer because you're adding 20% of the reduced price, not the original.

The calculator is mathematically precise. Results are displayed rounded to your chosen decimal places, but internal calculations use full precision.

Enter 15 for 15%. The calculator treats the percentage field as a percentage, not a decimal. It handles the division by 100 internally.

Ready to calculate?

Solve any percentage problem instantly with 5 specialized modes.

Open Percentage Calculator

Overview

Interface overview

Calculation mode section

Input values section (left)

CALCULATE button

Result section (right)

Bottom settings bar

5 Calculation modes

Percent of mode X% of Y

Select Percent of mode

Enter the percentage

Enter the number

View the result

Change mode % Increase/Decrease

Select Change mode

Enter the starting value

Enter the percentage change

View the new value

What percent mode X is Y% of Z

Select What percent mode

Enter the part (X)

Enter the whole (Z)

View the percentage

Difference mode % Between values

Select Difference mode

Enter the original value

Enter the new value

View the % difference

Reverse mode Find original

Select Reverse mode

Enter the final value

Enter the percentage change

View the original

Result & formula display

Settings & statistics bar

Auto-calculate toggle

Decimal places selector

CALCULATIONS counter

LAST RESULT display

MODE indicator

Practical examples

Frequently asked questions

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