How do you calculate percentage decrease?

Same formula — the answer will be negative. Example: (3,200 − 4,000) ÷ 4,000 × 100 = −20%, i.e. a 20% decrease.

What is the difference between percent change and percentage points?

Points are the gap between two rates (5% − 3% = 2 points). Percent change is relative: 2 ÷ 3 = +66.7%. Say which you mean.

Can percentage decrease exceed 100%?

Only when values cross zero or go negative. For positive quantities falling to zero, −100% is the floor (everything lost). Beyond that implies sign change.

Why is +50% then −50% not break-even?

Because bases differ. £100 +50% = £150; −50% of £150 = £75. Multipliers 1.5 × 0.5 = 0.75, so you are down 25% overall.

What if my old value is zero?

Percent change is undefined (division by zero). Report the absolute change and describe the base, e.g. '120 signups from a zero base'.

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Percentage Increase / Decrease Calculator

Old → new percent change, with increase vs decrease explained.

If your rent goes up from £900 to £1,020, is that a 12% rise or 13.3%? If sales drop from 4,000 to 3,200, is that a 20% fall or 25%? Percentage change compares a new value with an old one, and the answer depends on dividing by the right number. This calculator gives you the difference, the percentage change, whether it's an increase or a decrease, and the multiplier (for example 1.133×).

The rule is to divide by the old, starting value. That's why going from £50 to £75 is a 50% increase, but going back from £75 to £50 is a 33.3% decrease. The gap is the same £25, but the starting point is different. Businesses use percentage change to report growth, landlords and tenants use it in rent reviews, and investors use it to track returns.

Enter the old and new values above. Decimals, large numbers and negative values all work. The only case that can't be calculated is a starting value of exactly zero, and the calculator will explain why.

By DailyCalc Editorial Team · Updated 2026-10-03 · 6-min read · 3 sources cited

● % Change calculator

Math →

Percentage change formula

% change = (New − Old) ÷ |Old| × 100

Subtract to get the signed difference, divide by the magnitude of the starting value to normalise it, then scale by 100. A positive answer is an increase; negative is a decrease. The multiplier New ÷ Old tells you the growth factor: 1.20 means 120% of the original (a 20% rise).

Old: Starting value. Must be non-zero; its absolute value is the base.
New: Ending value after the change.
% change: Signed percent: +12.5% (increase) or −20% (decrease).

Worked example: £900 → £1,020 rent

A tenant's rent rises from £900 to £1,020. Landlord and tenant both want the correct percent:

Difference: 1,020 − 900 = +£120.
Divide by |Old|: 120 ÷ 900 = 0.13333…
Scale by 100: 0.13333 × 100 = 13.33% increase.
Multiplier: 1,020 ÷ 900 = 1.1333× — the new rent is 113.33% of the old.
Reverse check: 900 × 1.1333 ≈ 1,020 ✓.

Result: +£120 difference — a 13.33% increase (1.1333×).

How to use this calculator

Two boxes, one truth. Order matters: old first, new second.

Step 1: Enter the old value

The starting point — last month's sales, original price, opening weight. Cannot be zero.

Step 2: Enter the new value

The ending point. Can be higher, lower, equal, or even negative (e.g. profit → loss).

Step 3: Press Calculate

Read difference, signed % change, direction badge, and multiplier. Copy the steps for reports.

Step 4: Handle zero-start

If old is 0 (new product, new channel), report the absolute gain and note '% change undefined from zero' — auditors prefer honesty to infinity.

When to use it

Everyday situations where percentage change is the clearest way to describe a difference:

Sales and business

Month-on-month growth is (this month − last month) ÷ last month. If units sold go from 400 to 620, that's a 55% increase.

Rent and pay

A salary rise from £28,000 to £29,400 is 5%. Quoting both the amount and the percentage avoids confusion.

Health and fitness

Going from 82 kg to 76 kg is a 7.3% decrease. Percentages make progress easier to compare than raw numbers.

Investing

A share rising from 120p to 150p is up 25%, but falling back from 150p to 120p is down 20%. That's why a 50% loss needs a 100% gain to recover.

School results

Improving from 40 to 52 marks is a 30% improvement, even though the gap is only 12 marks.

Tips

Ways to present percentage changes clearly:

Give the amount as well as the percentage, for example '+13.3% (£120 a month)'.
When values cross from negative to positive, the percentage can be confusing, so lead with the actual difference.
Monthly changes don't simply add up over a year. 2% growth every month is about 26.8% over twelve months (1.02¹²), not 24%.
In a spreadsheet, =NEW/OLD−1 formatted as a percentage gives the change and is easy to check.
Round to one decimal place for most readers, and to two for money or scientific work.

Common mistakes

The errors behind most misleading percentage claims:

Dividing by the new value

(New − Old) ÷ New answers a different question. For percentage change, always divide by the old value.

Adding or averaging percentages

A 50% rise followed by a 50% fall doesn't take you back to where you started: 1.5 × 0.5 = 0.75, which is 25% down overall.

Claiming growth from zero

Going from 0 to 100 isn't an 'infinite' increase. Describe it as 100 new units from a starting point of zero.

Getting the sign wrong with negatives

A loss going from −50 to −30 is a 40% improvement. Divide by the size of the old value and describe the direction in words.

Sources & references

The formula, thresholds and guidance on this page were checked against these primary sources. Written and reviewed by DailyCalc Editorial Team; last updated 2026-10-03. Spotted an error? Tell us.

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