Sales went from 40,000 last month to 52,000 this month. That is good news, but “how much did we grow?” needs a number, not a feeling. The answer is 30%, and this guide shows exactly how to get there, how to handle the awkward cases, and how to avoid the comparisons that make growth look better than it was.
The sales increase formula
Increase % = ((New − Old) ÷ Old) × 100
Three steps: subtract to find the change, divide by where you started, multiply by 100 to express it as a percent.
Using the numbers above:
- 52,000 − 40,000 = 12,000 (the change)
- 12,000 ÷ 40,000 = 0.3 (the change relative to the starting point)
- 0.3 × 100 = 30%
The critical detail is step two: you divide by the old value, not the new one. Dividing by 52,000 would give 23.1%, which answers a different question entirely (what share of this month’s sales the growth represents). The starting point is always the denominator.
The third tab of the percentage calculator does this directly: enter the before value and the after value, and it returns the change as a percentage with the sign handled for you.
Worked examples
Growth
Q1 sales 250,000, Q2 sales 287,500.
(287,500 − 250,000) ÷ 250,000 × 100 = 37,500 ÷ 250,000 × 100 = 15% increase.
Decline
Sales fell from 90,000 to 76,500.
(76,500 − 90,000) ÷ 90,000 × 100 = −13,500 ÷ 90,000 × 100 = −15%, a 15% decrease.
The same formula covers both directions. A negative result is a decline; you do not need a separate “decrease formula”.
More than doubling
Sales rose from 20,000 to 65,000.
(65,000 − 20,000) ÷ 20,000 × 100 = 45,000 ÷ 20,000 × 100 = 225% increase.
Note that the new figure is 325% of the old one but the increase is 225%. Anything above 100% growth means the number more than doubled. Mixing up “of” and “increase” is a common reporting error.
Working backwards: what will next month be?
If you are targeting 12% growth on 85,000, multiply by 1.12:
85,000 × 1.12 = 95,200.
The shortcut is to add the growth rate to 1. For a 12% drop, multiply by 0.88 instead. The fourth tab of the percentage calculator does this in one step, which is handy for setting quotas from a baseline.
Four traps that distort growth numbers
1. The small base
Going from 2 sales to 6 is a 200% increase. Going from 2,000 to 6,000 is also a 200% increase. The percentage is identical; the achievement is not. Always report the absolute numbers alongside the percentage, especially when the starting figure is small.
2. Starting from zero
If last month was 0 and this month is 5,000, the formula breaks: you cannot divide by zero. There is no valid percentage increase from zero. Report it as “0 to 5,000” or “new” rather than inventing a figure like “infinite growth” or “100%”.
3. Comparing the wrong periods
A retailer comparing December to January will always look like it is collapsing. Compare like with like: this January against last January (year over year) rather than against last month. Month-over-month comparisons only make sense for businesses without a seasonal pattern.
4. Chaining percentages
A 10% increase followed by a 10% decrease does not return you to the start. 100,000 → 110,000 → 99,000. You end up 1% down, because the second percentage applies to a larger base. To find total growth across several periods, compare the first figure to the last one directly rather than adding the monthly rates together.
Growth in money vs. growth in profit
A 30% rise in revenue is not a 30% rise in profit. If costs grew faster, revenue growth can sit alongside a shrinking margin. Once you have the sales increase, it is worth checking the return side of the same period with the ROI calculator, and for ad-driven sales the ROAS calculator shows whether the extra revenue actually outpaced the spend that produced it.
If the growth came from a campaign, the per-result cost matters too. The CPA calculator shows what each acquisition cost, and the CPC calculator covers the click side.
Quick reference
- Formula: ((New − Old) ÷ Old) × 100
- Always divide by the old value. That is the baseline you grew from.
- Negative result = decline. Same formula, no special case.
- To project forward: multiply by (1 + rate), so +12% is × 1.12.
- Never compare against zero, and never add monthly percentages together.
To skip the arithmetic, the percentage calculator computes the change between any two values and shows whether it is a rise or a fall.