Percentage Calculator: five % modes, live online
Free percentage calculator with five modes in one tool: X% of Y, X is what % of Y, percent change, increase by %, and decrease by %. Results update live as you type.
What you'll use this for
Sales & discounts
"30% off $80" or "what % off if I pay $56?"
Grades & exams
Convert raw score to a percentage.
Tax & VAT
Add or remove a percentage cleanly.
Growth & trends
Compute period-over-period percent change.
How to use the percentage calculator
Pick a mode
Five real-world questions covered.
Type the numbers
Result is live — no submit button.
Read the result
Big headline plus a plain-English explanation underneath.
Frequently asked questions
Multiply Y by X/100. Example: 20% of 150 = 150 × 0.20 = 30.
((new − old) / old) × 100. Going from 80 to 100 is +25%; going from 100 to 80 is −20%.
Y × (1 ± X/100). Increasing 80 by 25% → 100. Decreasing 100 by 20% → 80. (Note: increasing then decreasing by the same % does NOT return to the start.)
Most calculator apps interpret the % key contextually (50 + 10% = 55, not 50.10). This tool spells out the mode so there’s no ambiguity.
About percentages
"Percent" comes from Latin per centum — "by the hundred." A percentage is just a fraction with a fixed denominator (100), which makes ratios easy to compare across different sizes.
The five common questions
- X% of Y — "What’s 18% of $84?"
- X is what % of Y — "$15 is what % of $200?"
- % change A→B — "Sales went from $80 to $100 — what % change?"
- Increase Y by X% — "Add 7% sales tax to $40."
- Decrease Y by X% — "Apply a 30% discount to $120."