Percentage Calculator

Percent, ratios, and percent change.

Math & NumbersUpdated 2026-04-05• Author: CalcDock Team, Math editor• Reviewed by: CalcDock Team, Editorial review: percentage vs percentage-point wording (Apr 2026)

Percentages appear in everyday decisions more often than most people realize: a 30% discount, a 7% sales tax, a 15% service tip, a 5% annual raise, a 12% investment return. This calculator handles the three most common percentage questions in one tool: finding X% of a number (e.g., 20% of $150 = $30), finding what percentage one number is of another (e.g., 45 out of 180 = 25%), and finding a value after a percentage increase or decrease (e.g., $80 after a 15% discount = $68). If you need to calculate how much something changed between two values — for example, a stock moving from $120 to $150 — use the Percentage Change Calculator instead. If you need to apply a percentage growth rate repeatedly over time, use the Compound Interest Calculator.

When this calculator helps most

Use for single-step “of / is what percent / increase-decrease” problems before compounding or multi-period growth.

What each input means

Percentage (X%) — The rate applied to a base (discount, tax portion, share). (%)
Base / whole — The number you take “percent of,” or the denominator for “what percent” questions. (any unit)
Part — The numerator when asking “what percent is A of B?” (same unit as whole)

Input mistakes to avoid

•“What percent is A of B?” uses A ÷ B × 100 — do not flip unless the question asks.
•For increase/decrease, confirm whether the change applies to the original base once.

Percentage Calculator

Percentage (X%)

Of Number (Y)

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Formula

X% of Y = (Y × X) ÷ 100 | X is what % of Y = (X ÷ Y) × 100 | Y after +X% = Y × (1 + X ÷ 100) | Y after −X% = Y × (1 − X ÷ 100)

Examples

20% of 250 — Discount Calculation

Finding a discount amount.

→ 20% of 250 = 50 | Sale price after 20% discount: 200

What percent is 36 of 144?

Exam score: 36 correct out of 144 questions.

→ 36 is 25% of 144

$450 after a 7% Sales Tax

Adding a percentage to a base price.

→ Tax: $31.50 | Total: $481.50

$80 after a 15% Discount

Finding the sale price after a percentage reduction.

→ Discount: $12 | Sale price: $68

What is 8.5% of $3,200?

Annual raise calculation — 8.5% raise on a $3,200 monthly salary.

→ 8.5% of 3,200 = 272 | New salary: 3,472/month

What is 18% of 240?

Basic percentage-of calculation.

→ 43.2

45 is what percent of 180?

Share of total.

→ 25%

How to read your results

→“X% of Y” answers how large a slice of Y corresponds to rate X.
→“A is what percent of B?” expresses A relative to B — always clarify which value is the base.
→Increase/decrease uses multipliers (1 ± rate) on the correct base — stacked discounts multiply, they do not add.
→Round only final displayed values when reporting; intermediate rounding can bias totals.

What this result means

Each mode answers one well-defined percent question — mix-ups between modes are the most common error.

Common Pitfalls

⚠️Confusing percentage with percentage points — a move from 3% to 5% is +2 percentage points, not a 2% increase.
⚠️Stacking discounts incorrectly — 30% off then 20% off is 44% off overall, not 50%.
⚠️Using the wrong base — after-discount calculations must use the reduced base, not the original.
⚠️Rounding too early — round at the end of the calculation to avoid compounding errors.

Tips

✓To find 10% of any number, move the decimal point one place to the left. Build other percentages from there: 5% = half of 10%, 20% = double 10%.
✓For a percentage increase, multiply by (1 + rate). For a decrease, multiply by (1 − rate). This is faster than calculating the change and adding/subtracting.
✓Percentage and percentage points are different things. A rate rising from 2% to 3% is a 1 percentage point increase, but a 50% increase in the rate.
✓When comparing discounts, a 30% discount followed by an additional 20% discount is not the same as 50% off — it is 44% off: 0.70 × 0.80 = 0.56.
✓Use the Percentage Change Calculator for before-and-after comparisons. Use this calculator for single-step percentage questions.

How to check your results

✓Plug round numbers (10% of 100 = 10) to verify mode selection.

Warnings & Limitations

⚠️For before/after comparisons, use a percent change calculator — not a simple percent of.
⚠️When reporting results, state whether values are rounded and to how many decimals.

What this calculator does not tell you

–Compound growth over multiple periods — use compound interest.
–Percentage points vs relative percent change — see guides and percent-change tool.

Frequently Asked Questions

How do I find X% of a number?

Multiply the number by X and divide by 100. Example: 20% of 150 = 30.

How do I find what percent X is of Y?

Divide X by Y and multiply by 100. Example: 45 of 180 = 25%.

Sources & References

Report an issue with this calculator

Editorial & review note

This page stays narrow: “what percent of what” and the three-value triangle—structural change, tax, and stacked sale scenarios link out to dedicated tools to avoid one bloated form.

Editorial Policy