Math Tools
Find the percentage decline from an original value to a new, lower value.
Percentage Decrease
25%
From 200 to 150, a change of 50.
Percentage decrease = (Original − New) ÷ Original × 100
Percentage decrease is a measure of how much a value has gone down, expressed as a percentage of the original amount. If an item cost £100 and now costs £75, the percentage decrease is 25%. It's the opposite of percentage increase and helps you understand the scale of a drop in human terms rather than just the raw number.
The calculator subtracts the new value from the original value to find the drop amount, then divides that drop by the original value and multiplies by 100 to get a percentage. This percentage shows what fraction of the original value was lost. You can enter the original and new values, and the tool instantly shows the percentage drop and the absolute amount lost.
Percentage Decrease = ((Original Value - New Value) / Original Value) × 100Original Value is what something was worth or cost before the change. New Value is what it is now. The result is the percentage decrease. A larger percentage means a steeper drop.
| Input | Result | Notes |
|---|---|---|
| Original: £200 | New value: £150 | Percentage decrease = 25% | The item dropped by £50, which is 25% of the original £200 price. A typical sale discount. |
| Original: 80 kg | New weight: 72 kg | Percentage decrease = 10% | A 10% weight loss is often viewed as significant progress and measurable health improvement. |
| Original: 1,000 shares at £5 each | Now worth £4.25 each | Percentage decrease = 15% | A 15% stock price drop is painful but not uncommon in volatile markets. Helps you assess portfolio damage. |
Percentage increase measures how much something went up from the original (e.g., £100 to £120 is 20% increase). Percentage decrease measures how much it went down (e.g., £100 to £80 is 20% decrease). The formula is the same shape, just subtracting in the opposite direction.
Because the second 50% is calculated from the new lower value. £100 drops 50% to £50. A 50% increase on £50 is only £25, giving you £75 total—not £100. Percentage changes are always relative to the base you're working from.
No. A percentage decrease maxes out at 100% when the new value is zero (the item is completely gone). If the new value is somehow negative or the original was zero, the maths breaks—this calculator assumes both values are positive and original is larger.
If a jumper was £80 and is now £60, the percentage decrease is 25%. That 25% is the discount amount. In real stores, they often advertise '25% off' without saying what the original price was, which makes it hard to judge value.
That's an increase, not a decrease. The calculator will give you a negative percentage (e.g., -25%), which means the value went up by 25%. Use a percentage increase calculator instead for clarity, or just note that the value grew rather than shrank.
You can't. Division by zero breaks the formula. If you started with zero, there's no baseline to measure a percentage from. This tool is for situations where you have a real starting value.