Percentage decrease calculator:
measure a drop against where you started

What percentage decrease means

Percentage decrease measures a drop relative to the value you started with. It answers a simple question: of what I had, what share is gone?

That framing is useful for price cuts, falling electricity bills, shrinking sales and drop-offs in website traffic, where the rupee or unit figure alone does not tell you how serious the fall is.

Because the base is the original value, percentage decrease lets you compare different items fairly. A ₹300 drop on a ₹2,000 item is 15%, while the same ₹300 on a ₹1,200 item is 25%. The rupee drop is identical, but the second is the bigger fall in proportion.

The original value is always the base. Dividing by the new, smaller figure overstates the drop.

Percentage decrease formula

Percentage decrease problems usually give you two values and ask for a single rate. The easiest way to avoid slips is to write the three quantities in a column: old, new and the drop. Then divide the drop by the old value.

1. 1Subtract the new value from the old value to get the drop.
2. 2Divide the drop by the old value.
3. 3Multiply by 100 and add the % sign.

A decrease can never be more than 100% for values that start positive and stay non-negative, since you cannot lose more than everything.

A handy cross-check is to apply the answer back to the original: ₹2,000 reduced by 15% is ₹2,000 × 0.85 = ₹1,700, which matches the new price. If your check does not land on the new value, the percentage is wrong.

Watch the sign. If the new value is higher than the old, the formula returns a negative decrease, which is really an increase. Switch to percentage increase wording instead of reporting a negative drop.

It helps to sanity-check any result against simple landmarks. A fall of 50% means the value halved, a fall of 25% means a quarter has gone, and a fall of 10% means one tenth is gone. If your answer is far from the landmark you expect, the base is probably wrong.

Worked examples: a price cut and a lower bill

The same formula works for bills. A monthly electricity bill that falls from ₹4,500 to ₹3,780 is down by ₹720, which is 16% of the original.

The same method suits a shrinking business metric. If a shop sold 480 units in March and 396 in April, the drop is 84 units and 84 ÷ 480 × 100 = 17.5%.

These examples all use one recipe, so comparing a ₹300 fall on one item with ₹720 on another is no harder than comparing 15% and 16%.

When comparing two decreases, compare percentages, not rupees. A ₹720 fall on a ₹4,500 bill is 16%, a larger proportional drop than ₹300 on ₹2,000 at 15%, even though ₹720 is the bigger number in rupees.

Working backwards: new value or original value

Sometimes you know the rate and need a value. Multiply by (1 − rate) to find the new figure, or divide by (1 − rate) to recover the original.

A ₹2,000 item cut by 15% costs ₹2,000 × 0.85 = ₹1,700. Going the other way, a sale price of ₹1,700 that includes a 15% cut came from ₹1,700 ÷ 0.85 = ₹2,000.

Do not work out 15% of the sale price and add it back. That gives ₹1,955, which is not the original, because 15% of ₹1,700 is smaller than 15% of ₹2,000.

This reverse calculation is useful when a shop shows only the sale price and the percentage off. You can recover the "was" price and judge whether the offer is meaningful by comparing it with what the item cost earlier.

How big a rise undoes a drop?

Once a value has dropped, the base is smaller, so the same percentage rise does not bring you back. The rise needed is the drop divided by what is left.

People often assume a 20% fall can be undone by a 20% rise. The arithmetic says otherwise: ₹1,000 down 20% is ₹800, and 20% of ₹800 is only ₹160, so you reach ₹960.

This is why a 50% fall in a price or a share needs the value to double before it is back where it started. Larger drops are far harder to recover than their percentage suggests.

The table also works in reverse. If a price has risen 25%, a fall of 20% takes it back to where it began. The two are linked: if a rise is x, the fall that undoes it is x ÷ (1 + x).

In planning, this is why avoiding a large loss matters more than the headline percentage suggests. A 40% fall needs a rise of 66.67% (40 ÷ 60) to recover.

Mistakes that change the answer

• Dividing by the new value: ₹300 ÷ ₹1,700 gives 17.65%, not 15%.
• Treating a drop of 15 percentage points as a 15% decrease; they are different measures.
• Using the wrong base in a series of drops, since each percentage applies to the previous price.
• Calculating a decrease from zero, which is undefined; report the absolute drop instead.
• Forgetting the direction: if the new value is higher, the result is an increase, not a decrease.

Most errors come from the wrong base, so before you divide ask which number was there first. If you cannot tell, you are probably comparing two peers with no before and after, and the percentage difference guide is the better tool.

For both rises and falls with the same formula, see the percentage change guide. If you only need X% of a number, the percentage calculator guide covers that.