Daily Life

Percentage Calculator

Q: How do I mentally calculate a 10% discount?

**Divide the price by 10 and subtract it from the original**. If something costs $1,000, 10% is $100, the final price is $900. You can also multiply by 0.9: `1,000 x 0.9 = 900`.

Q: Does a 20% increase followed by a 20% discount leave me at the same price?

**No**. `100 + 20% = 120`. `120 - 20% = 96`. You lose **4%** in the process. Percentages don't add and subtract linearly because the second percentage is applied to a new amount.

Q: How do I calculate price variation or inflation?

`((new_price - old_price) / old_price) x 100`. If a product went from $100 to $150, the inflation was **50%**. If it went from $150 to $100, the change is **-33.3%**.

Q: What is a 'percentage point' vs a 'percentage'?

If a rate goes from **50% to 55%**, it rose **5 percentage points**. But in relative terms, it rose **10%** (`5/50 x 100`). Media outlets often confuse these when reporting rate changes or election results.

Q: How do I calculate selling price to cover cost with a 30% margin?

If your cost is $700 and you want a 30% margin, **DON'T multiply by 1.30** — that gives you margin on cost (markup). For margin on sale price, use `price = cost / (1 - margin)` = `700 / 0.70 = $1,000`. Margin on sale = 30%.

Q: How do I calculate a stacked discount (20% + 10%)?

Multiply the factors: `(1 - 0.20) x (1 - 0.10) = 0.80 x 0.90 = 0.72`. You pay **72% of the original price**, which equals a **total discount of 28%** (not 30%).

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Reviewed by: Martín Rodríguez (política editorial ) · Last reviewed: 20 may 2026

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The percentage (from Latin per centum, 'per hundred') is the workhorse of US daily math: calculating sales tax at checkout, the 18–20% restaurant tip customary in the US, salary raises, mortgage rates from the Federal Reserve, commission, inflation tracked by the Bureau of Labor Statistics (BLS) CPI, and Black Friday discounts. This calculator handles five scenarios: (1) X% of Y, (2) price after discount, (3) price after increase, (4) what % is X of Y, and (5) percentage change between two values. It shows the formula used in each case — the same operations behind every US credit-card APR statement and IRS withholding calculation.

Last reviewed: May 19, 2026 Verified by Martín Rodríguez Source: US Bureau of Labor Statistics — Consumer Price Index (CPI), IRS — Tax Withholding & Estimator, NIST Digital Library of Mathematical Functions, Khan Academy — Percentages 100% private

When to use this calculator

You're buying something on sale and want to know the final price.
You're offered a salary raise of X% and want to calculate the new salary.
You're comparing two prices and want to know the percentage change.
You need to calculate a commission, tip, or sales tax on an amount.
You're studying math and want to verify your calculations.

Example: 25% off a $1,200 US laptop on Black Friday

Mode: Price after discount.
Value 1 (price): $1,200 USD.
Value 2 (discount %): 25.
Formula: final_price = price − (price × discount / 100).
Calculation: 1,200 − (1,200 × 25 / 100) = 1,200 − 300.
Result: final price $900 USD, discount $300 USD (before US state sales tax).

Result: With 25% off, you pay $900 USD and save $300 USD (sales tax applies on top of $900 in most US states).

How it works

2 min read

5 Percentage Calculation Modes

1. Simple Percentage: X% of Y

result = (Y x X) / 100

Example: What is 15% of 100? → (100 x 15) / 100 = 15.

You can also multiply by the decimal form: 100 x 0.15 = 15.

2. Price After Discount

final_price = price x (1 - discount/100)

Example: $1,000 with 20% off → 1,000 x (1 - 0.20) = 1,000 x 0.80 = $800.

3. Price After Increase

final_price = price x (1 + increase/100)

Example: $1,000 with a 20% increase → 1,000 x 1.20 = $1,200.

4. What Percentage Is X of Y

percentage = (X / Y) x 100

Example: 25 is ___% of 100 → (25 / 100) x 100 = 25%.

5. Percentage Change

change = ((final - initial) / initial) x 100

Example: from $100 to $150 → ((150 - 100) / 100) x 100 = +50%.

If change < 0, it's a decrease; if > 0, an increase.

Quick Equivalence Table

Percentage	Fraction	Decimal	Mental Shortcut
5%	1/20	0.05	Divide by 20
10%	1/10	0.10	Move decimal one place left
20%	1/5	0.20	Divide by 5
25%	1/4	0.25	Divide by 4
33%	1/3	0.33	Divide by 3
50%	1/2	0.50	Divide by 2
75%	3/4	0.75	x 3, / 4
100%	1/1	1.00	The number itself

Mental Math Tricks for Percentages

1. 10% of anything: move the decimal point one place left (10% of 250 = 25).
2. 5% of anything: 10% divided by 2.
3. 1% of anything: move the decimal two places left (1% of 2500 = 25).
4. X% of Y = Y% of X: 15% of 80 is the same as 80% of 15 = 12.
5. Add 10%: multiply by 1.1.
6. Subtract 10%: multiply by 0.9.

Common Mistakes

1. Adding percentages directly: a product with a 20% increase + 20% discount does NOT return to the original price. $100 → $120 → $96. You lost 4%.
2. Confusing change with difference: if something went from 100 to 150, the change is +50% (not +50).
3. Applying percentage on the tax-included total: if a final price is $121 with 21% tax included, the tax is NOT 21% of $121. It's 121 / 1.21 = 100 base + $21 tax.
4. Stacked discounts: 20% + 20% is NOT 40% total. It's (1 - 0.20) x (1 - 0.20) = 0.64 → 36% total discount.
5. Confusing percentage points with percentages: if a rate goes from 50% to 55%, it rose 5 percentage points (or 10% relative change).

Frequently asked questions

How do I mentally calculate a 10% discount?

Divide the price by 10 and subtract it from the original. If something costs $1,000, 10% is $100, the final price is $900. You can also multiply by 0.9: 1,000 x 0.9 = 900.

Does a 20% increase followed by a 20% discount leave me at the same price?

No. 100 + 20% = 120. 120 - 20% = 96. You lose 4% in the process. Percentages don't add and subtract linearly because the second percentage is applied to a new amount.

How do I calculate price variation or inflation?

((new_price - old_price) / old_price) x 100. If a product went from $100 to $150, the inflation was 50%. If it went from $150 to $100, the change is -33.3%.

How do I extract tax from a price that already includes it?

If the final price is $121 with 21% tax included, the pre-tax price is 121 / 1.21 = $100 and the tax is $21. It's NOT 21% of $121 (that would give $25.41).

What is a 'percentage point' vs a 'percentage'?

If a rate goes from 50% to 55%, it rose 5 percentage points. But in relative terms, it rose 10% (5/50 x 100). Media outlets often confuse these when reporting rate changes or election results.

How do I calculate selling price to cover cost with a 30% margin?

If your cost is $700 and you want a 30% margin, DON'T multiply by 1.30 — that gives you margin on cost (markup). For margin on sale price, use price = cost / (1 - margin) = 700 / 0.70 = $1,000. Margin on sale = 30%.

How do I calculate a stacked discount (20% + 10%)?

Multiply the factors: (1 - 0.20) x (1 - 0.10) = 0.80 x 0.90 = 0.72. You pay 72% of the original price, which equals a total discount of 28% (not 30%).