Rent went from $1,500 to $1,725. The landlord called it "a small adjustment." The math disagrees.
Use this free percent change calculator to find the percentage increase or decrease between two values. Enter the old value and the new value and get the change as a percentage — for prices, salaries, weight, traffic, revenue, test scores, or anything else that moved.
The direction is built in: a positive result is an increase, a negative one is a decrease. The trap is the base. Percent change is always measured against where you started, which is why a 50% drop needs a 100% rise to get back to even.
What This Percent Change Calculator Does
- Calculates percent increase and percent decrease in one formula
- Returns a signed result, so direction is unambiguous
- Works for salary raises, price hikes, growth rates, and weight change
- Different from percent difference, which has no direction — see the percent difference calculator
How to Use the Percent Change Calculator
Inputs:
- Old Value — the starting or earlier value (this is the base)
- New Value — the ending or current value
Steps:
- Enter the original value first — getting these backwards flips the answer
- Enter the new value
- Click Calculate
- Positive means increase, negative means decrease. For the absolute gap regardless of direction, use percent difference
How the Calculation Works
Percent Change = (New − Old) ÷ Old × 100
- The denominator is always the old value. Swap them and you get a different number: 50→75 is +50%, but 75→50 is −33%
- Decreases cannot exceed −100% (nothing left), while increases have no ceiling
- Percentage points are not percent: moving from 10% to 15% is +5 points and a +50% change. Both are correct and they mean different things
- Back-to-back changes multiply: −20% then +20% leaves you at 0.8 × 1.2 = 0.96, i.e. 4% down
Worked Example: Rent from $1,500 to $1,725
- Difference: 1,725 − 1,500 = 225
- Divide by the old value: 225 ÷ 1,500 = 0.15
- × 100 = +15%
- To get back to $1,500 from $1,725 would need a 13% decrease, not 15%. The base changed, so the percentage did too. This asymmetry is why "we gave it all back" rarely means what people think.
Tips (From People Who Have Made These Mistakes)
- Always ask "percent of what?" A 100% increase in a tiny number is still a tiny number
- For multi-year growth, use CAGR rather than a single percent change: (End ÷ Start)^(1/years) − 1
- Comparing a raise to inflation? A 3% raise during 3% inflation is flat — check the inflation calculator
- When the old value is zero, percent change is undefined. Report the absolute change instead of dividing by zero
Frequently Asked Questions
How do you calculate percent change?
Subtract the old value from the new, divide by the old, and multiply by 100: (New − Old) ÷ Old × 100. From 80 to 100 is (20 ÷ 80) × 100 = +25%.
How do you calculate percent increase?
Same formula — a positive result *is* the increase. From $50 to $65: (15 ÷ 50) × 100 = +30%.
How do you calculate percent decrease?
Same formula, negative result. From 200 to 150: (−50 ÷ 200) × 100 = −25%. Report it as "a 25% decrease."
What is the difference between percent change and percent difference?
Percent change has a direction and uses the original value as the base. Percent difference compares two values with no before/after, dividing by their average. Use change for time series, difference for comparisons.
Why does a 50% loss need a 100% gain to recover?
Because the base shrank. $100 down 50% is $50; getting from $50 back to $100 is a $50 gain on a $50 base, which is 100%. This is exactly why large drawdowns hurt more than they look.
Mini Roast Disclaimer
We roast the number, not you. "Only a 15% increase" is a sentence that has only ever been said by the person collecting it.
Reality Check
The formula is exact; the interpretation is where mistakes live. Confirm which value is the base, watch for percentage points versus percent, and be suspicious of any percentage quoted without its starting number — a 200% increase in something meaningless is still meaningless.