Percentage Calculator

What is a percentage?

A percentage expresses a value as parts per hundred. A percentage calculator solves the three questions built on it: X% of Y, X is what percent of Y, and percent change from X to Y.

How this calculator works

• Tab 1 — X% of Y: enter a percent and a value to get the portion. 20% of 150 returns 30 — the math behind discounts, tips, and tax.
• Tab 2 — X is what % of Y: enter two values to find the share. 30 and 150 returns 20% — test scores, market share, goal progress.
• Tab 3 — percent change calculator: enter a start and end value. From 50 to 65 returns +30% in green; drops show red, with the absolute change alongside.
• No setup: pick a tab, type the numbers, and the answer updates instantly — nothing to sign up for.

How to use the result

1. Shopping or tipping: apply it. If 20% of $150 is $30, the sale price is $150 − $30 = $120; a 20% tip makes the bill $180.
2. Checking a share: sanity-check Tab 2’s answer. If the first value is smaller than the second, the percent must land under 100 — otherwise the inputs are swapped.
3. Reading growth: pair the percent with the absolute change shown beside it. “+50%” sounds dramatic, but $2,000 to $3,000 is really a $1,000 story — quote both.
4. Pricing or goals: run it backwards. A 50% markup on a $40 cost means a $60 price — multiply the cost by 1.5 (that is, 1 + 50 ÷ 100).
5. Splitting macros: set your calorie target with a TDEE calculator, then budget each macro here — 30% protein on 2,000 calories is 600 calories, about 150 g of protein.

What is a percentage calculator?

A percentage calculator is three tools in one set of tabs: a straightforward percent calculator for “X% of Y”, a what-percent-of calculator for shares, and a percentage increase calculator for growth or decline. The formulas underneath are short: multiply the value by the percent ÷ 100 to get X% of Y; divide X by Y and multiply by 100 to get the share; subtract the old value from the new, divide by the old value, and multiply by 100 to get percent change.

Common mistakes

• Wrong base. Percent change divides by the starting value. 50 → 65 is +30%, but the return trip 65 → 50 is -23.1%, not -30%.
• Percent vs. percentage points. A rate moving from 4% to 6% rose 2 percentage points but grew 50%. The change tab reports the relative figure — know which one you’re quoting.
• Assuming increases and decreases cancel. Up 20% then down 20% doesn’t return to the start: 100 → 120 → 96. Chain the steps instead of netting them.
• Expecting compound math. The change tab measures one step. It doesn’t compute CAGR for multi-year growth or percent error for lab work — those use different formulas.

Percentages rarely come alone — you usually stack a discount, add tax, then split the bill. For that follow-up arithmetic, pass the result to a basic calculator.