What is X% of Y — for discounts, commissions, percentage of a total. 20% of 150 → 30 . X is what % of Y — for "score / max" style ratios. 30 of 150 → 20% . % change — signed: positive is an increase, negative is a decrease. 100 → 125 = +25% . Increase / Decrease — applies a percentage adjustment to a starting value. Tip / Tax — convenience for adding a percentage on top of a bill.

Percentage change isn't symmetric. Going 100 → 125 is +25%; going 125 → 100 is −20%, not −25%. The denominator is the starting value, which differs in each direction. Stacking percentages compounds. A 20% increase followed by a 20% decrease doesn't return you to the start (1.20 × 0.80 = 0.96, a net 4% loss). For sequential markups/discounts, calculate each step. Tip on pre-tax vs post-tax. Convention varies by country and venue. The tool computes the percentage of the value you enter — pick which value you actually want as the base. Rounding. Output is rounded to 6 decimals then trimmed; if you need legal/accounting precision (banker's rounding, currency-specific rules), do that step in your domain layer, not here.

Percentage points vs percent change is the number-one news-article error. "Interest rates rose from 4% to 5%" is a 1 percentage-point increase but a 25% relative increase. "Unemployment fell from 8% to 6%" is a 2 percentage-point drop but a 25% relative drop. Headlines routinely use "percent" to mean "percentage points," which understates change. When you see one, do the relative-change calculation mentally — it's often the more meaningful number. Order matters when stacking changes. Markdowns and markups don't commute. A 20% markup followed by a 20% markdown gives 0.96 of original — a 4% net loss. Sequential percentage operations multiply (1.20 × 0.80), not add. This trips up retail pricing ("our 30% off the 20% markup is back to original" — no, it's down 16%) and tax calculations alike. "Average percent" is rarely what you want. Investment returns of +10%, +10%, −20% over three years give an arithmetic mean of 0% but a geometric mean of −1.4% — your actual portfolio is down. CAGR (compound annual growth rate) uses the geometric mean and is the honest number for multi-period growth or return reporting. Anyone advertising portfolio performance using arithmetic means is shading the truth. The "of" matters: percent of what. "Tax goes up 2% next year" → 2% of what? Of current rate (so 20% → 20.4%)? Of income (a flat 2 percentage point increase)? Of the tax bill (20% → 20% × 1.02 = 20.4%)? News headlines about tax changes often leave this ambiguous; the difference matters by a factor of 10+. Always pin down the base. Percentage point spreads in interest rates affect monthly payments non-linearly. On a 30-year mortgage at 6%, going to 7% adds ~10% to the monthly payment. Going from 6% to 8% adds ~22%. Going from 6% to 5% saves ~10%. Small-sounding rate moves have large-sounding payment moves — this is why central-bank rate decisions move so much downstream economic activity.

Percentage Calculator

Five percentage calculators in one: of, what %, increase/decrease, change, and tip/tax.

Calculation

Result

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What is this for?

Six different "percentage" calculations come up daily and are easy to mix up: how much is X% of Y? What percent is X out of Y? What's the change between two values? Apply a markup or discount? Tip or tax? Each is a slightly different formula, and getting them confused leads to wrong invoices, wrong discounts, and embarrassing reviews. This tool runs all six side by side with the formula spelled out, so you can pick the right one and double-check the maths.

What each mode does

What is X% of Y — for discounts, commissions, percentage of a total. 20% of 150 → 30.
X is what % of Y — for "score / max" style ratios. 30 of 150 → 20%.
% change — signed: positive is an increase, negative is a decrease. 100 → 125 = +25%.
Increase / Decrease — applies a percentage adjustment to a starting value.
Tip / Tax — convenience for adding a percentage on top of a bill.

Common gotchas

Percentage change isn't symmetric. Going 100 → 125 is +25%; going 125 → 100 is −20%, not −25%. The denominator is the starting value, which differs in each direction.
Stacking percentages compounds. A 20% increase followed by a 20% decrease doesn't return you to the start (1.20 × 0.80 = 0.96, a net 4% loss). For sequential markups/discounts, calculate each step.
Tip on pre-tax vs post-tax. Convention varies by country and venue. The tool computes the percentage of the value you enter — pick which value you actually want as the base.
Rounding. Output is rounded to 6 decimals then trimmed; if you need legal/accounting precision (banker's rounding, currency-specific rules), do that step in your domain layer, not here.

Expert notes

Percentage points vs percent change is the number-one news-article error. "Interest rates rose from 4% to 5%" is a 1 percentage-point increase but a 25% relative increase. "Unemployment fell from 8% to 6%" is a 2 percentage-point drop but a 25% relative drop. Headlines routinely use "percent" to mean "percentage points," which understates change. When you see one, do the relative-change calculation mentally — it's often the more meaningful number.
Order matters when stacking changes. Markdowns and markups don't commute. A 20% markup followed by a 20% markdown gives 0.96 of original — a 4% net loss. Sequential percentage operations multiply (1.20 × 0.80), not add. This trips up retail pricing ("our 30% off the 20% markup is back to original" — no, it's down 16%) and tax calculations alike.
"Average percent" is rarely what you want. Investment returns of +10%, +10%, −20% over three years give an arithmetic mean of 0% but a geometric mean of −1.4% — your actual portfolio is down. CAGR (compound annual growth rate) uses the geometric mean and is the honest number for multi-period growth or return reporting. Anyone advertising portfolio performance using arithmetic means is shading the truth.
The "of" matters: percent of what. "Tax goes up 2% next year" → 2% of what? Of current rate (so 20% → 20.4%)? Of income (a flat 2 percentage point increase)? Of the tax bill (20% → 20% × 1.02 = 20.4%)? News headlines about tax changes often leave this ambiguous; the difference matters by a factor of 10+. Always pin down the base.
Percentage point spreads in interest rates affect monthly payments non-linearly. On a 30-year mortgage at 6%, going to 7% adds ~10% to the monthly payment. Going from 6% to 8% adds ~22%. Going from 6% to 5% saves ~10%. Small-sounding rate moves have large-sounding payment moves — this is why central-bank rate decisions move so much downstream economic activity.