Percentage Calculator
Calculation type
Share with friends
How to use
- 1 Choose a mode: X% of Y, X is what % of Y, or % change between two values.
- 2 Enter the two numbers required by the mode.
- 3 Click Calculate to see the result and a plain-English explanation.
- 4 Switch tabs to recalculate with a different mode using related numbers.
- 5 For percent change, enter the original value first and the new value second — a positive result means an increase.
About Percentage Calculator
FAQ
Q How do I calculate a 20% tip on a $45 bill?
Multiply the bill by 0.20 (or move the decimal one place left and double): $45 × 0.20 = $9. For 18% (more common in some regions), multiply by 0.18 = $8.10. For quick estimation, round 20% as "double the tax" — most US states have sales tax around 7–10%, so doubling roughly approximates 18–20%.
Q How do I calculate sales tax on a purchase?
Multiply the pretax price by your state and local combined rate. For a $100 item with 8% combined rate: $100 × 0.08 = $8 tax, total $108. For working backwards from a total, divide: a $108 receipt at 8% rate has a pretax price of $108 / 1.08 = $100.
Q What is the difference between percent and percentage points?
A percent is a relative comparison. A percentage point is the absolute difference between two percentages. If unemployment rises from 4% to 5%, that is a 1 percentage point rise but a 25% relative increase. Mortgage and credit card APR changes are typically reported in percentage points; investment returns in percent change.
Q How do I find percent change between two numbers?
Subtract the old value from the new value, divide by the absolute value of the old value, and multiply by 100. Going from 100 to 130 is (130 − 100) / 100 × 100 = +30%. A negative result is a decrease. Going from 100 to 70 is −30%.
Q If a stock goes down 20% then up 20%, am I back where I started?
No — you're at 96% of the original. A 20% loss takes $100 to $80; a 20% gain on $80 only adds $16, ending at $96. To recover from a 20% loss requires a 25% gain. From a 50% loss requires a 100% gain. This asymmetry is why volatility hurts long-term returns.
Q What does 200% increase mean?
The new value is three times the original. A 100% increase doubles; 200% triples; 300% quadruples. Many marketing claims confuse "200% increase" with "twice as much" — they're different. When in doubt, restate as a multiplier (×3) to remove ambiguity.
Q Can the starting value in percent change be zero?
No. Percent change is undefined when the starting value is zero, because dividing by zero is undefined. Use absolute change ($0 → $50 = +$50, not +∞%) or rephrase the comparison ("started from zero" instead of a percent).
Q What grade is 18 out of 24 questions correct?
(18 / 24) × 100 = 75%, which is a C in most US grading schemes (where 90+ = A, 80-89 = B, 70-79 = C, 60-69 = D, below 60 = F). Curved grading or schools with stricter scales (90+ = A, 87-89 = A−) may differ — check your syllabus.
Official resources
Khan Academy: Intro to percents
Free Khan Academy lessons covering percentages from the basic concept to applications.
IRS — Tax tables and brackets
IRS Publication 17 — Your Federal Income Tax, including current tax brackets in percent.
BLS: Calculating consumer price index changes
US Bureau of Labor Statistics fact sheet on percent change vs. percentage points in economic data.
NIST Engineering Handbook — Percentages
NIST Engineering Statistics Handbook on percentage calculations and ratios in measurement.