Percentage Decrease Calculator

Percentage decrease measures how far a value has fallen relative to where it started. The rule is the drop divided by the original, times 100, which is what statisticians call a percentage change with the sign flipped: Eurostat's glossary writes percentage change as (later ÷ earlier − 1) × 100, so a fall shows there as a negative change, and this calculator reports the size of that fall as a positive percentage. Sale prices, depreciation and rate cuts all use it. Enter the original and new values and the calculator returns the decrease, the amount lost, and the share of the original that remains.

A 150 item on sale for 100 has fallen by 50, which is 33.33% of 150, and the buyer is still paying 66.67% of the original price. A 25,000 car worth 17,500 three years on has lost 30%. The retained figure is the same information seen from the other side: 100 minus the decrease.

Two decreases can only be compared as percentages when their starting points are comparable. A 15% fall from 80,000 is 12,000, while a 15% fall from 800 is 120, and the percentage alone hides a hundredfold difference. The amount lost, shown next to the percentage, keeps that difference in view.

Run it with sensible defaults

With an original value of 150 and a new value of 100, the decrease is 33.33%, the amount lost is 50, and 66.67% of the original is retained. The defaults are a starting point rather than a recommendation.

The levers in this calculation

The two inputs do not pull equally, and how unequally depends on how close together they are. At the defaults, a 1% rise in the original value (150 to 151.5) lifts the decrease from 33.33% to 33.99%, about 2% in relative terms, and a 1% rise in the new value (100 to 101) cuts it to 32.67%, again about 2%. When the gap is narrower the sensitivity grows: with 150 falling to 140, the result is 6.67%, and a 1% nudge on either input moves it by roughly 14%. Small decreases are fragile numbers.

How the maths works

Decrease equals original minus new. Percentage decrease equals the decrease divided by the original, times 100. Retained equals 100 minus that percentage. When the new value sits above the original, the sign turns negative and the calculator relabels the result as a percentage increase rather than reporting a negative decrease.

Why a fall and the rise that undoes it are different sizes

A fall and the recovery from it are measured against different bases, which is why they never match. Falling from 150 to 100 is a 33.33% decrease, but climbing back from 100 to 150 is a 50% increase, because the rise is measured against the smaller number. A 50% drop needs a 100% rise to undo; a 20% drop needs 25%; a 10% drop needs 11.11%. The same asymmetry is why a further 50% off after 50% off is not free: 150 halved twice is 37.50, a 75% decrease, not 100%. Eurostat's note on percentage points covers the neighbouring confusion, where a rate falling from 12% to 10% has dropped 2 percentage points but 16.67% in relative terms.

Worked example

A property valued at 500,000 at purchase is appraised at 425,000 five years later. The decrease is 75,000, the percentage decrease is 15%, and the property has retained 85% of its original valuation. The calculator surfaces all three figures at once, which makes it straightforward to line up several properties or several dates side by side.

Common scenarios

• Retail and e-commerce: checking an advertised discount against the marked-down price
• Asset depreciation: tracking how vehicles, equipment or property values fall over time
• Market performance: measuring the percentage drop in a holding or a portfolio from its peak
• Salary or wage changes: putting a pay reduction into percentage terms
• Subscription and service costs: sizing a price reduction between plans or providers
• Health metrics: expressing a fall in a test result or clinical measurement as a percentage

What the result shows

Three outputs. The percentage decrease is the proportional drop from start to finish. The absolute decrease, in your currency, is the amount actually lost. The retained percentage is what is left of the original, and it is the figure that answers the question when what remains matters more than what has gone.

What the result does not capture

This calculation is static; it measures change between two fixed points and says nothing about volatility, seasonal variation or future direction. The percentage decrease alone does not indicate whether a decline is likely to reverse, stabilise or accelerate. Cause is invisible in the arithmetic: a 20% drop could reflect a genuine loss, a one-off sale price, temporary market conditions or a measurement error. The calculator also ignores context, since the same percentage decrease carries different implications depending on timeframe, sector and starting value.

For educational illustration

This tool estimates percentage decrease for learning and comparison. Results are arithmetic based on the inputs entered and serve to illustrate the concept. They are not forecasts, valuations or advice for any real transaction.