Percentage Calculator
A flexible percentage calculator for everyday U.S. use — discounts at the register, raises, mortgage rate moves, sales tax, or working out what percentage one number is of another. Pick the operation, plug in the numbers, and get the answer plus the working so you can sanity-check it.
How is this calculated?
The calculator handles four common operations. Percentage of a value: V × p/100. Reverse (find the whole given a part and percent): part / (p/100). Percentage change: (new − old) / old × 100. Percentage increase or decrease: V × (1 ± p/100). Sales-tax additions and removals are special cases — adding 8% sales tax multiplies by 1.08; removing it divides by 1.08, not by 0.92 (a common error).
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. So 15% of $80 is 80 × 15 ÷ 100 = $12. The shortcut: move the decimal in the percentage two places left (15% → 0.15) and multiply: 80 × 0.15 = $12. Quick mental math for tipping and discounts.
How do I work out percentage change?
(New − Old) ÷ Old × 100. If your salary rises from $65,000 to $70,000, that's (70,000 − 65,000) ÷ 65,000 × 100 = 7.69%. A negative answer is a decrease. Always divide by the original value, not the new one.
Why isn't a 20% drop reversed by a 20% rise?
Because the base changes. $100 down 20% is $80; up 20% from $80 is only $96. To recover from a 20% loss you need a 25% gain. This bites investors hard — losses hurt more than equivalent-percentage gains help, which is why preserving capital matters.
How do I remove sales tax from a price?
Divide by (1 + tax rate), not by (1 − tax rate). A $108 price including 8% sales tax is 108 ÷ 1.08 = $100 net, with $8 of tax. Sales tax rates vary by state, county, and city, so check your local rate before doing the math.
Last updated: May 2026 · Rates sourced from IRS