Percentage Calculator
Percent increase, decrease, discounts, margins, and more.
Enter your numbers and get an instant result—no sign-up, no ads tracking your inputs, no server involved.
Standard Percentage
Part to Whole
Percentage Change
What Each Calculation Mode Does
Most percentage questions fall into one of five types. Here is what each one means and when you would actually use it.
Percent of a Number
Result = (Percentage ÷ 100) × Number
15% of $340 = $51
Use when: Calculating a tip, a discount amount, a tax, or a commission.
Percent Increase
((New − Old) ÷ Old) × 100
$80 → $100 = 25% increase
Use when: Measuring salary growth, price changes, revenue growth year-over-year.
Percent Decrease
((Old − New) ÷ Old) × 100
$100 → $75 = 25% decrease
Use when: Calculating a discount, a drop in headcount, or a reduction in expenses.
Percentage Difference
(|A − B| ÷ ((A + B) ÷ 2)) × 100
$80 vs $100 = 22.2% difference
Use when: Comparing two separate values with no clear 'before' and 'after'—like two product prices or two competitors' scores.
Reverse Percentage (Find the Original)
Original = Final ÷ (1 + Rate)
$115 after 15% markup → original = $100
Use when: Finding the pre-tax price, the pre-markup wholesale cost, or the base salary before a raise was applied.
Three Percentage Mistakes That Cost Real Money
Percentages are intuitive until they are not. These are the errors that trip up smart people most often.
1. The Sequential Discount Trap
A sale sign reads "30% off, then an extra 20% off at checkout." It feels like 50% off. It is not.
Sequential percentages compound. They never simply add.
2. Markup vs. Margin Confusion
A retailer buys a product for $60 and sells it for $100. They say "we mark things up 40%." But their profit margin is actually only 40%—wait, is it?
Markup uses cost as the base. Margin uses revenue. Both describe the same $40 profit—in very different ways.
3. The Loss-Recovery Asymmetry
A portfolio drops 50%. To recover, it needs to go back up 50%. Right?
Losses and gains are not symmetrical because the base changes after a loss.
Who Uses This and How
Salary & Raise Negotiations
Calculate the real value of a raise against inflation. A 3% raise when inflation is 4.5% is effectively a pay cut of about 1.4% in purchasing power.
Retail & E-commerce
Check whether your sale pricing still covers costs. The margin calculator helps you confirm profitability before pushing a discount live.
Students & Exam Scores
"I got 73 out of 85—what percentage is that?" or "What score do I need on the final to pass with a 70%?" Paste your numbers and find out instantly.
Freelancers & Invoicing
Calculate the percentage of a project budget used, apply a late fee, or figure out your effective hourly rate after platform fees.
Finance & Investing
Track the percentage return on a position, calculate dividend yield, or compare two portfolio growth rates over a period.
Budgeting & Personal Finance
Apply the 50/30/20 rule to a paycheck, find out what percentage of income goes to rent, or track month-over-month spending changes.
Percentage vs. Percentage Points — a Distinction Worth Knowing
This is one of the most misused concepts in financial news and everyday conversation.
Suppose a central bank raises interest rates from 4% to 6%.
Both are technically correct—they measure different things. Saying "rates rose 50%" and "rates rose 2 percentage points" are two valid descriptions of the same event.
Tips for Getting Accurate Results
- Always identify your base. Percent increase uses the old value as the base. Percent difference uses the average of both values. Choosing the wrong one changes your result entirely.
- Do not add sequential percentages. Apply them one at a time. 10% off, then 10% off again ≠ 20% off (it is 19%).
- Check sign direction. A negative result in percent change means a decrease. If you expect a loss and get a positive number, you may have swapped old and new values.
- Use reverse percentage for pre-tax prices. If a receipt shows a total including tax, divide by (1 + tax rate) to find the pre-tax amount—not subtract the percentage.
- Context matters more than the number. A 10% growth rate is impressive for a mature business and underwhelming for an early-stage startup. Always state the base when sharing a percentage.
Frequently Asked Questions
What is the formula for percent increase?
((New Value − Old Value) ÷ Old Value) × 100. Example: price goes from $50 to $65. ((65 − 50) ÷ 50) × 100 = 30% increase.
Can a percent decrease ever exceed 100%?
No. A decrease is capped at 100%, which represents losing everything (reaching zero). You cannot lose more than 100% of a value. Increases, however, have no ceiling.
How do I find what percentage one number is of another?
(Part ÷ Whole) × 100. So 45 out of 60 is (45 ÷ 60) × 100 = 75%.
Why can't I just average two percentages?
Because percentages are relative to different bases. Division A's 10% growth on $1M revenue adds $100k. Division B's 20% growth on $100k adds $20k. Averaging 10% and 20% to get 15% ignores the fact that the bases are very different. You need to calculate the total absolute change across both bases first.
Is the calculator accurate for very small or very large numbers?
Yes. The tool uses standard JavaScript floating-point arithmetic with rounding guards to avoid the tiny decimal drift (like 0.1 + 0.2 = 0.30000000000000004) that can appear in raw binary math.
Understand the spread of your data with the Standard Deviation Calculator or track your academic standing with the GPA Calculator.