Percentage Calculator

When to use this calculator

Percentages show up in daily American life more than almost any other piece of math, and this page rolls the five most common jobs into one tool. Grab it when you are figuring an 18% tip at a restaurant, checking the real price on a 25% clearance rack, adding sales tax to a cart total, or turning a raise quoted as a percentage into actual dollars. Each tab handles one kind of question, so you pick the one that fits.

The fundamental jobs are: finding X% of a number (18% of a $50 check), finding what percent one number is of another ($30 out of $150 is 20%), and measuring a percentage increase, decrease, or change between two values. Together they cover tips, discounts, sales tax, GPA-style scoring, and pay bumps — the percentage questions that come up at the register and on the paycheck, not once a year.

Reading your result

Each mode hands back a slightly different kind of number. The percent-of tab returns a dollar amount — 18% of $50 is $9. The what-percent tab returns a proportion — $30 of $150 is 20%. The change tab returns a signed figure: $100 to $150 is +50%, and $100 to $50 is −50%, with the sign showing whether it rose or fell.

Watch the gap between a percent and a percentage point. If a credit card APR moves from 5% to 8%, that is a 3 percentage-point jump but a 60% relative increase. Both are accurate; they answer different questions. The change tab here always works in relative terms, so enter 5 and 8 and you will get +60%, not +3 — handy for spotting when a headline number is being framed to sound bigger or smaller than it is.

A worked example

Picture a $50 dinner check where you want to leave 18%. Put $50 in the value box and 18 in the percent box on the percent-of tab and you get $9. To see the grand total, switch to Add/Subtract %, add 18% to $50, and it returns $59. Split between two people that is $29.50 each.

For a shopping example, a $80 jacket on a 25% clearance: enter $80 and 25 on the Add/Subtract tab, choose subtract, and you get $60 with a $20 saving shown. If the receipt only listed the $60 sale price and you wanted the original ticket, Reverse % takes $60 as 75% of the original and returns $80.

Mistakes to watch for

Most percentage slip-ups come from working off the wrong base or mixing up relative change with percentage points.

• Confusing a percentage change with percentage points — 5% to 8% is +3 points but +60% in relative terms.
• Trying to undo a 25% markup by subtracting 25% — $100 plus 25% is $125, but $125 minus 25% is $93.75, not $100. To reverse it you divide by 1.25.
• Tipping on the post-tax total when you meant to tip on the pre-tax subtotal — it changes the amount.
• Assuming two percentage changes add up — a 10% gain followed by a 10% loss leaves you below where you started.

Everyday US percentage uses

Two percentages dominate American spending: the tip, customarily 15 to 20% on restaurant service, and sales tax, which is added at checkout and varies by state and locality rather than being baked into the shelf price. Use the percent-of tab for the tip and the Add/Subtract tab to add your local sales-tax rate to a subtotal. Because the sticker price excludes tax, the Reverse % tab is also useful for backing the pre-tax amount out of a total.

Beyond tips and tax, percentages run through discounts and clearance pricing, loan and credit-card APRs, 401(k) contribution rates, and grades — including the percentage scores that feed a GPA. Whenever a number is quoted as a percent, one of the five tabs above will convert it into the dollar figure you actually need.