ToolStack › Percentage Calculator
Math Tool

PERCENT
AGE

Six types of percentage calculation in one place. Discounts, tips, grade changes, tax — all instant, no calculator needed.

What is X% of Y?
01 / 06
e.g. "What is 15% of $80?" → "$12"
What is % of ?
12
15% of 80 = 12
X is what % of Y?
02 / 06
e.g. "45 is what % of 200?" → "22.5%"
is what % of ?
22.5%
45 is 22.5% of 200
Percentage Change
03 / 06
e.g. "From $50 to $65" → "+30% increase"
From to
+30%
30% increase (+15)
Discount / Sale Price
04 / 06
e.g. "20% off $120" → "$96 sale price, $24 saved"
% off
$96
Sale price · You save $24
Add Percentage (Tax / Tip)
05 / 06
e.g. "$85 + 18% tip" → "$100.30 total, $15.30 tip"
+ %
$100.30
Tip: $15.30
X% of what equals Y?
06 / 06
e.g. "25% of what = 40?" → "160"
% of what equals
160
25% of 160 = 40

Percentage Formula

Percentage = (Part ÷ Whole) × 100. To find a percentage of a number: multiply the number by the percentage and divide by 100. e.g. 15% of 200 = 200 × 15 ÷ 100 = 30.

Percentage Change

Change % = ((New − Old) ÷ Old) × 100. A positive result is an increase; negative is a decrease. e.g. from 80 to 100: ((100−80)÷80)×100 = 25% increase.

Reverse Percentage

To find the original value before a percentage was applied: Original = Final ÷ (1 + rate). e.g. if a price is $110 after 10% tax, the pre-tax price is $110 ÷ 1.10 = $100.

Common Percentages

10% = divide by 10 · 25% = divide by 4 · 20% = divide by 5 · 50% = divide by 2 · 33.3% = divide by 3 · 75% = multiply by 0.75. Mental math shortcuts for everyday use.

FAQ
How do I calculate a percentage in my head? ▾
For 10%, move the decimal one place left. For 5%, halve that. For 15%, add 10% and 5% together. For 20%, divide by 5. For 25%, divide by 4. Most everyday percentages (tax, tips, discounts) can be estimated using these building blocks.
What is percentage vs percentage points? ▾
These are different! If an interest rate goes from 3% to 4%, it increased by 1 percentage point, but the percentage change is 33% (1 is 33% of 3). Percentage points measure absolute differences between two percentages; percentage change measures relative change.
How do I calculate a tip? ▾
Use calculator #5 above. Or mentally: for 20%, divide the bill by 5. For 18%, calculate 20% and subtract 10% of that. For 15%, calculate 10% and add half. On a $60 bill: 20% tip = $12. 15% tip = $6 + $3 = $9.
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📋 Calculation History
Your recent percentage calculations, saved automatically.
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How to Use the Percentage Calculator

Calculate any percentage, percentage change, or reverse percentage instantly.

01
Choose your calculation type
Select from: 'What is X% of Y?', 'X is what % of Y?', '% change from X to Y', or 'X increased/decreased by Y%'. Pick the one that matches your question.
02
Enter your numbers
Fill in the two values you know. The third value calculates automatically as you type — no need to press Enter.
03
Read the result
The answer appears immediately with a plain-English explanation of what was calculated and why.
04
Use percentage change for comparisons
Great for comparing prices, salaries, or metrics year-over-year. A positive result is an increase; negative is a decrease.
💡
💡 Quick mental check: to find 15% of any number, find 10% (move decimal left one place) then add half of that. 15% of $240 = $24 + $12 = $36.