Percentage Decrease Calculator
Calculate percentage decrease, increase, percentage difference and find original values. Includes formulas and worked examples.
Last updated: February 2026
Percentage Decrease Calculator
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About This Calculator
This free UK percentage calculator covers four common percentage calculations: percentage decrease, percentage increase, percentage difference (using the symmetric formula), and finding the original value before a percentage reduction. All calculations are performed instantly in your browser.
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How to Work Out Percentage Decrease: Formulas and Worked Examples
Percentage decrease (and increase) calculations come up constantly in everyday UK life — from working out how much you have saved in a sale, to understanding whether your energy bill has gone up or down, to calculating whether a salary offer represents a real-terms improvement. This guide explains all three core formulas clearly, with plain-English explanations and real UK examples.
The Percentage Decrease Formula
Percentage Decrease = ((Original − New) / Original) × 100
To determine percentage decrease between two values:
- Subtract the new (lower) value from the original value
- Divide the result by the original value
- Multiply by 100 to get the percentage
Worked Example 1 — House price drop:
A house was listed at £350,000 and sold for £330,000.
Decrease = £350,000 − £330,000 = £20,000
Percentage Decrease = (£20,000 / £350,000) × 100 = 5.71%
The house sold for 5.71% below the asking price.
Worked Example 2 — Sale discount:
A jacket originally priced at £120 is reduced to £84 in the sales.
Decrease = £120 − £84 = £36
Percentage Decrease = (£36 / £120) × 100 = 30%
You are saving 30% — so this is a genuine 30%-off sale price.
The Percentage Increase Formula
Percentage Increase = ((New − Original) / Original) × 100
The formula for how to work out increase in percentage is the mirror of the decrease formula — you subtract the original from the new value instead, and the result will be positive (showing growth).
Worked Example 3 — Salary increase:
You earn £32,000 and receive a pay rise to £34,500.
Increase = £34,500 − £32,000 = £2,500
Percentage Increase = (£2,500 / £32,000) × 100 = 7.81%
With UK inflation at approximately 2.6% (February 2026), this represents a real-terms pay increase of around 5.2%.
Worked Example 4 — Energy bill increase:
Your quarterly gas bill rose from £280 to £315.
Increase = £315 − £280 = £35
Percentage Increase = (£35 / £280) × 100 = 12.5%
Your gas bill has increased by 12.5%.
The Percentage Difference Formula
Percentage Difference = |V1 − V2| / ((V1 + V2) / 2) × 100
Percentage difference is used when you want to compare two values without implying that one came "before" the other. It uses the average of the two values as the base, making it symmetric — the percentage difference between A and B is always the same as the percentage difference between B and A.
This is different from percentage change, which uses the original value as the base and implies a direction (increase or decrease). Use percentage difference when comparing two equal-status values such as two shop prices, two test scores, or two survey results.
Worked Example 5 — Comparing two quotes:
Builder A quotes £8,500 for a kitchen extension; Builder B quotes £11,000.
Average = (£8,500 + £11,000) / 2 = £9,750
|Difference| = £11,000 − £8,500 = £2,500
Percentage Difference = (£2,500 / £9,750) × 100 = 25.64%
The two quotes differ by 25.64%.
Finding the Original Value Before a Percentage Decrease
Original = New Value ÷ (1 − Decrease% / 100)
This reverse calculation is useful when you know the final price and the discount percentage, and want to find out what the original price was before the reduction.
Worked Example 6 — Working back from a sale price:
An item costs £68 after a 15% reduction. What was the original price?
Original = £68 / (1 − 15/100) = £68 / 0.85 = £80
The original price was £80. You saved £12.
Worked Example 7 — Property under offer:
A house sold for £425,000, which was 8% below the asking price. What was the asking price?
Original = £425,000 / (1 − 8/100) = £425,000 / 0.92 = £461,957
The asking price was approximately £462,000.
Quick Percentage Change Reference Table
| Original | New Value | % Change | Direction |
|---|---|---|---|
| 100 | 75 | −25% | Decrease |
| 100 | 50 | −50% | Decrease |
| 200 | 150 | −25% | Decrease |
| £50,000 | £55,000 | +10% | Increase |
| £1,200 | £1,440 | +20% | Increase |
| £250,000 | £237,500 | −5% | Decrease |
Percentage Change in UK Everyday Life
Property prices: UK house prices rose by approximately 4.4% in the year to December 2025, according to the ONS House Price Index. If your home was worth £280,000 a year ago, a 4.4% increase would put the current value at £292,320.
Council Tax: Many UK councils are permitted to increase Council Tax by up to 5% per year (3% core plus 2% adult social care). On a Band D bill of £2,100, a 5% increase adds £105, bringing the annual total to £2,205.
Retail discounts: When a shop advertises 20% off, you pay 80% of the original price. An item labelled £65 at 20% off costs £65 × 0.80 = £52. Alternatively, use the reverse formula to check: £52 / 0.80 = £65 original price.
Salary negotiations: If you are offered a salary of £38,000 for a role you currently earn £35,000 for, the percentage increase is ((38,000 − 35,000) / 35,000) × 100 = 8.57%. With UK inflation running at approximately 2.5–3% in early 2026, this represents a meaningful real-terms pay rise of around 5.5–6%.
Energy bills: The UK energy price cap is set quarterly by Ofgem. When the cap changes, you can use the percentage increase formula to calculate the exact impact on your estimated annual bill and budget accordingly.
Common Mistakes When Calculating Percentage Change
Mistake 1: Using the wrong base
When calculating percentage change, always divide by the original value, not the new value. For percentage difference, divide by the average of the two values. Dividing by the new value gives a different (and usually incorrect) answer.
Mistake 2: Confusing percentage points with percentage change
If interest rates rise from 4% to 5%, that is a 1 percentage point increase, but a 25% percentage increase in the rate. These are very different figures. Always be clear about which you mean.
Mistake 3: Treating successive percentage changes as additive
A 20% decrease followed by a 20% increase does not return you to the original value. Example: £100 − 20% = £80; £80 + 20% = £96, not £100. Sequential percentage changes must be calculated step by step.
Frequently Asked Questions
How do I calculate percentage decrease?
Use the formula: Percentage Decrease = ((Original − New) / Original) × 100. Subtract the new (lower) value from the original, divide by the original value, and multiply by 100. For example: original 200, new 160 → (200−160)/200 × 100 = 20% decrease.
What is the percentage difference formula?
The percentage difference formula is: |V1 − V2| / ((V1 + V2) / 2) × 100. It uses the average of the two values as the denominator, making it symmetric (the result is the same whichever value you call V1 or V2). This distinguishes it from percentage change, which uses the original (starting) value as the base.
How do you work out increase in percentage?
Percentage Increase = ((New − Original) / Original) × 100. Subtract the original value from the new value, divide by the original value, and multiply by 100. A positive result means an increase; a negative result means a decrease. Example: from 50 to 75 → (75−50)/50 × 100 = 50% increase.
How do I find the original price before a percentage reduction?
Use the formula: Original = New Value / (1 − Decrease% / 100). For example, if an item now costs £60 after a 25% discount: Original = £60 / (1 − 25/100) = £60 / 0.75 = £80. The "Find Original" tab of our calculator handles this instantly.
What is the difference between percentage decrease and percentage difference?
Percentage decrease measures how much a value has fallen relative to the original value. Percentage difference measures the relative gap between two values relative to their average. Use percentage decrease (or increase) when there is a clear "before" and "after". Use percentage difference when comparing two values of equal standing, such as two prices or two measurements.
Can percentage decrease be more than 100%?
No — a value cannot decrease by more than 100% of itself, as that would mean it falls below zero. A 100% decrease means the value reaches exactly zero. If a value crosses zero (e.g., profits turning into a loss), it is not meaningful to express this as a simple percentage decrease; instead, describe it as a change from a positive to a negative value.
How do I figure out the percentage difference between two prices?
To figure out percentage difference between two prices, use: |Price A − Price B| / ((Price A + Price B) / 2) × 100. For example, between £90 and £110: |90−110| / ((90+110)/2) × 100 = 20/100 × 100 = 20%. Our "% Difference" tab calculates this instantly.
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