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'.

Math · Free tool

Percentage Increase / Decrease Calculator

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

Did your rent rise from £900 to £1,020 — is that 12% or 13.3%? Did sales fall from 4,000 to 3,200 — a 20% drop or 25%? Percentage change is the maths of before-and-after, and getting the denominator right is everything. This calculator takes an old value and a new value and returns the absolute difference, the signed percent change, whether it is an increase or decrease, and the multiplier (e.g. 1.133×).

The rule is simple but often broken: always divide by the old (starting) value, using its absolute value. That is why going £50 → £75 is +50%, but reversing £75 → £50 is −33.3% — the journey matters, not just the gap. Businesses use this for growth reporting, landlords for rent reviews, teachers for progress, and investors for returns. Misstating it can mislead customers or breach advertising rules, so showing your working is not pedantry — it is compliance.

Enter old and new numbers above. Negative inputs, decimals and large figures are fine. The only undefined case is starting from exactly zero, which the tool will flag with a plain-English explanation and a workaround.

Updated 2026-09-01 · 6-min read · Formula + steps included

● % Change workstation

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.

Real use cases

Where signed percent change is the required language:

Retail & ecommerce

'Revenue +18.2% MoM' uses (this month − last month) ÷ last month. Promotions are measured the same way: units 400 → 620 is +55%.

Rent & salaries

UK rent reviews and pay rises are negotiated in percent change. £28,000 → £29,400 is +5.0% — quote both £ and % to avoid ambiguity.

Fitness & health

Weight 82 → 76 kg is −7.3%. Body-fat, cholesterol and 5K times all read better as percent change than raw gaps.

Investing

A stock 120p → 150p is +25%; back 150p → 120p is −20%. Asymmetry is why a −50% loss needs +100% to recover.

Classroom progress

Test 40 → 52 marks is +30% improvement even though the gap is 12 marks. Teachers use both to motivate fairly.

Pro tips

Present change like an analyst:

Always pair % with absolute: '+13.3% (£120/mo)' beats either alone.
For falls over 100% with negatives crossing zero, show the £ gap prominently — percents confuse.
Annualise short sprints: +2% a month ≈ +26.8% a year (1.02¹²), not 24%.
Use multipliers in spreadsheets: =NEW/OLD−1 formatted as % is auditable.
Round to 1 decimal for people, 2 for money and science.