Percentage Increase/Decrease Calculator
Whether you're tracking a price hike, a salary bump, or a drop in test scores, this calculator gives you the exact percentage change between any two numbers. Enter your original value and new value — or apply a known percentage change to a starting number — and get the result in seconds. No guesswork, no rounding errors.
When to use this calculator
- Calculating how much a product's price increased or decreased after a sale or price change
- Determining the percentage raise (or cut) in a salary or hourly wage
- Measuring improvement or decline in test scores, KPIs, or sports statistics
- Comparing year-over-year revenue or expense changes in a business report
- Figuring out how much weight, distance, or time changed as a percentage
- Applying a known percentage change (e.g., +15%) to a starting value to find the new number
How it works
2 min readWhat is percentage increase and decrease?
Percentage increase or decrease measures the relative change between two values expressed as a percentage of the original amount. The formula is ((new−old)/old)×100. For example, a change from $100 to $120 equals a 20% increase, while $100 to $80 equals a 20% decrease. This metric shows proportional change rather than absolute difference.
How It Works
Percentage change expresses how much a quantity has grown or shrunk relative to its original value. The two core formulas are:
Formula 1 — Find the % Change
% Change = ((New Value − Original Value) / Original Value) × 100Formula 2 — Apply a Known % Change
New Value = Original Value × (1 + (% Change / 100))To find only the added/subtracted amount:
Difference = Original Value × (% Change / 100)---
Worked Examples
| Scenario | Original | New | % Change |
|---|---|---|---|
| Price increase | $100 | $120 | +20% |
| Price decrease | $100 | $80 | −20% |
| Salary raise | $55,000 | $60,500 | +10% |
| Weight loss | 200 lb | 185 lb | −7.5% |
| Score drop | 95 | 76 | −20% |
Example walkthrough — $100 to $120:
% Change = ((120 − 100) / 100) × 100
= (20 / 100) × 100
= 20% → IncreaseExample walkthrough — apply +15% to $200:
New Value = 200 × (1 + 0.15)
= 200 × 1.15
= $230
Difference = $30---
Important Notes & Limitations
Percentage change vs. percentage points: If an interest rate rises from 2% to 3%, that is a 1 percentage-point increase but a 50% increase in the rate itself. These are different concepts — this calculator computes percentage change, not percentage-point difference.
Zero as the original value: Division by zero is undefined. If your original value is 0, percentage change cannot be calculated mathematically. The calculator will return an error for this input.
Symmetry is not reversible: A 20% increase followed by a 20% decrease does NOT return to the original value. Example: $100 → $120 (+20%) → $96 (−20%). Keep this in mind when chaining percentage changes.
Negative original values: The formula still works algebraically, but interpret the sign with caution (e.g., a temperature or financial loss moving from −$50 to −$25 shows a 50% increase in the value, even though the absolute magnitude decreased).
Frequently asked questions
What is the formula for percentage increase?
% Increase = ((New Value − Original Value) / Original Value) × 100. For example, going from $80 to $100: ((100 − 80) / 80) × 100 = 25% increase. The original (starting) value is always the denominator.
What is the formula for percentage decrease?
It's the same formula: ((New − Original) / Original) × 100. When the new value is smaller, the result is negative, indicating a decrease. Example: $100 to $75 = ((75 − 100) / 100) × 100 = −25%.
Is a 50% increase the same as a 50% decrease in reverse?
No. If a price rises 50% from $100 to $150, a 50% decrease from $150 brings it to $75 — not $100. To reverse a P% increase, you need to decrease by P/(1+P/100) percent.
What's the difference between percentage change and percentage points?
Percentage points measure the arithmetic difference between two percentages (e.g., 5% to 8% = +3 percentage points). Percentage change measures the relative change ((8−5)/5×100 = 60%). Always clarify which one you mean in financial or statistical contexts.
Can I calculate percentage change when the original value is negative?
Mathematically yes, but interpret carefully. If original = −$200 and new = −$100, the formula gives 50% increase in value. Whether that's meaningful depends on context (e.g., reducing a debt is a positive outcome despite a positive % change sign).
How do I apply a percentage increase to a number?
Multiply the original by (1 + rate). For a 15% increase: New Value = Original × 1.15. For a 15% decrease: New Value = Original × 0.85. You can also compute the difference alone: Difference = Original × (rate / 100).
Why can't I calculate percentage change from zero?
Because the formula divides by the original value. Division by zero is mathematically undefined — any number divided by 0 has no meaningful result. If your starting point is zero, you can only state the absolute change, not a percentage.
What does a 100% increase mean?
A 100% increase means the value doubled. Original × (1 + 1.00) = Original × 2. Example: $50 increased by 100% = $100. A 200% increase means it tripled: $50 → $150.
How is this different from a percentage of a number?
A 'percentage of' (e.g., 20% of $500 = $100) gives you a portion of one number. Percentage change compares two different values — it measures how much one number moved relative to another. They use different formulas and answer different questions.
Is the percentage increase from $80 to $100 the same as from $100 to $80?
No. $80 to $100 is a 25% increase ((20/80)×100). $100 to $80 is a 20% decrease ((−20/100)×100). The original (base) value is different in each case, so the percentage magnitudes differ even though the absolute change is $20 in both.