A percentage increase or decrease adjusts a starting value by a given proportion. Unlike the percentage change calculator (which tells you what percentage something changed by), this tool applies a known percentage to produce a new value. It's the forward calculation — you know the rate, and you want the result.
The formulas
For an increase, the multiplier is greater than 1. For a decrease, it's less than 1. A 25% increase means you multiply by 1.25. A 25% decrease means you multiply by 0.75.
Worked examples
- Salary raise: A $60,000 salary with a 5% raise → $60,000 × 1.05 = $63,000. The raise amount is $3,000.
- Price reduction: A $250 item marked down 30% → $250 × 0.70 = $175. You save $75.
- Population growth: A town of 12,000 grows by 8% → 12,000 × 1.08 = 12,960. That's 960 new residents.
- Budget cut: A $500,000 budget reduced by 12% → $500,000 × 0.88 = $440,000. The cut is $60,000.
Common uses in everyday life
- Salary and pay: Calculate your new monthly take-home after a percentage raise or cost-of-living adjustment.
- Rent increases: Landlords often raise rent by a fixed percentage each year. Know your new monthly amount before signing the lease.
- Inflation: If inflation is 3.5%, find out what today's $100 purchase will cost next year: $100 × 1.035 = $103.50.
- Exam scores: Some exams apply a curve by increasing all scores by a fixed percentage.
Why a 50% increase and 50% decrease don't cancel out
This is one of the most counter-intuitive facts about percentages. If you increase $100 by 50%, you get $150. If you then decrease $150 by 50%, you get $75 — not $100. The reason is that the base changes. The 50% increase was calculated on $100, but the 50% decrease was calculated on $150. Each percentage operation uses the current value as its reference, not the original one.