What's 15% of 200? What percent is 45 of 300? What's the percentage increase from 50 to 75? Three common questions, one quick tool. Step-by-step answers.
Percentage change is one of the most common calculations in daily life. Below is a reference table showing how to calculate percentage increase, decrease, and reverse percentages for common scenarios.
| Scenario | Old Value | New Value | Formula | Result |
|---|---|---|---|---|
| Price increase | $50 | $62 | ((62-50)/50)×100 | 24% increase |
| Salary raise | $60,000 | $65,000 | ((65,000-60,000)/60,000)×100 | 8.3% increase |
| Stock decline | $100 | $75 | ((75-100)/100)×100 | 25% decrease |
| Discount off | $80 | $60 | ((60-80)/80)×100 | 25% off |
| Reverse: original price | $72 sale | 20% off | 72÷(1-0.20) | $90 original |
Remember that a 50% increase followed by a 50% decrease does NOT return to the original value ($100 → $150 → $75). Always calculate percentage changes sequentially, not by adding or subtracting percentages. For reverse percentages, divide the final value by (1 - discount rate) to find the original price.
Mental math for percentages is a practical life skill. Here are quick techniques for calculating common percentages without a calculator, along with examples of how they apply to real-world situations.
| Percentage | Mental Math Trick | Example | Real-World Use |
|---|---|---|---|
| 10% | Move decimal point one place left | 10% of $85 = $8.50 | Tip baseline, 10% discount |
| 15% | 10% + half of 10% | 15% of $85 = $8.50 + $4.25 = $12.75 | Standard restaurant tip |
| 20% | 10% x 2 | 20% of $85 = $8.50 x 2 = $17.00 | Great service tip, 20% off sale |
| 25% | Divide by 4 | 25% of $200 = $50 | Quarter off, large discount |
| 5% | 10% divided by 2 | 5% of $85 = $8.50 / 2 = $4.25 | Sales tax in some states |
| 8% | 10% - 2% (1% x 2) | 8% of $85 = $8.50 - $1.70 = $6.80 | Common sales tax rate |
| 1% | Move decimal point two places left | 1% of $85 = $0.85 | Fine-tuning calculations |
Practice these mental math shortcuts to handle tips, discounts, and tax calculations in seconds. For a 15% tip on a $68 bill: 10% = $6.80, half is $3.40, total = $10.20. For a 20% off $45 item: 10% = $4.50, double = $9.00 off, pay $36.00. Use this percentage calculator for precise calculations when you need exact numbers.
Interest rates, poll results and unemployment figures are already expressed as percentages, so a change in them is measured in percentage points — not percent. Mixing the two up inflates or shrinks a change by an order of magnitude, and it is the most common error in rate-based reporting and rate shopping.
When the Federal Reserve cuts by 25 basis points, the target rate moves 0.25 percentage points. If the rate was 5.00%, that cut is a 5% relative reduction in the cost of money, not 0.25%. The same arithmetic applies to mortgage shopping: moving from 6.00% to 6.50% is half a percentage point, but it is an 8.3% increase in the interest you pay — about $95 more per month on a $300,000 30-year loan.
| Starting value | New value | Change in points | Relative change |
|---|---|---|---|
| 5.00% rate | 6.00% rate | 1.00 point | +20% |
| 6.00% mortgage rate | 6.50% mortgage rate | 0.50 point | +8.3% |
| 8.00% levy | 8.25% levy | 0.25 point | +3.1% |
| 44% in a poll | 46% in a poll | 2 points | +4.5% |
| 4.0% unemployment | 4.4% unemployment | 0.4 point | +10% |
Use percent change when the underlying quantity is a count, a price or a balance — anything that is not already a rate. A $50 product rising to $62 is a 24% increase. A 5.00% rate rising to 6.00% is a 1-point increase. The quick test is the unit: dollars, people, units, sessions mean percent change; percent, APR, APY, basis points and rate mean points.
Lenders advertise in points because half a point sounds trivial; your budget feels it in percent. Savings accounts work the same way in reverse: 4.00% to 4.75% is a 0.75 point move, but it is 18.75% more interest on the same balance. Run both numbers before you switch accounts or refinance — the points tell you what changed, the percent tells you whether it matters.
$100 today won't be $100 in 10 years. See how inflation eats into your savings and investments using CPI-based projections. Your money's real value, year by year.
Exactly how old are you — down to the day, hour, and minute? Calculate your chronological age, the difference between any two dates, or how many days until your next birthday.
Dinner's over and the check arrives — time to do math. Or just use this. Enter the total, pick a tip percentage or custom amount, split among friends, and optionally round up. Done.
Add tax to a purchase, strip it from a total, or look up any US state's combined rate. Updated for 2026 with state and local rates. No more guessing at the register.
What are the odds? Calculate single-event probability, the chance of at least one success in multiple tries, and expected value. From coin flips to real-world decisions.