Percentage change without the confusion: a guide for reports and spreadsheets

Percentage change is one of the simplest calculations and one of the most commonly botched. Reports mix up the base, confuse percentage points with percentages, and describe the same movement in two different ways. A few rules fix most of this.

The formula

Percentage change = (new value − old value) ÷ old value × 100

The old value is always the denominator. If it is zero, the percentage change is undefined, and you should show the rupee change instead.

Rule 1: know your base

If monthly sales go from ₹80,000 to ₹92,000, the change is 12,000 ÷ 80,000 = 15%. Dividing by the new value (12,000 ÷ 92,000 = 13%) gives the wrong answer for “growth”. Whether you are looking at growth over a year or over a quarter, keep the earlier figure as the base.

Rule 2: percentage points are not percentages

If a company’s operating margin goes from 12% to 15%, it rose by 3 percentage points. In percentage terms, the margin rose 25% (3 ÷ 12). Both statements are true, but they say very different things, and writing “rose 3%” is ambiguous. State which one you mean.

Rule 3: gains and losses are not symmetrical

A fall of 20% followed by a rise of 20% does not bring you back. 100 falls to 80, and 20% of 80 is 16, giving 96. To recover from a 20% fall you need a 25% rise (20 ÷ 80). To recover from a 50% fall, you need 100%.

Rule 4: percentages do not add across different bases

A price that rises 10% one year and 10% the next has risen 21% in total (1.1 × 1.1 = 1.21), not 20%. If you need an average, use CAGR rather than the simple mean of the percentages. For an average rate across years, a CAGR calculator does the work.

Rule 5: show the amounts too

A 200% rise from ₹1 crore to ₹3 crore is ₹2 crore. A 5% rise on ₹500 crore is ₹25 crore. In a report, place the rupee change next to the percentage so readers can judge the scale.

Spreadsheet tips

• Use a formula such as =(B2-A2)/A2 and format the cell as a percentage; do not multiply by 100 and also use the percent format.
• Guard against blanks and zeros with an IF test.
• Label the columns clearly: old, new, change, % change.
• When showing declines, make sure the sign is shown.

Awkward cases

• From a loss to a profit. If a company goes from −₹10 crore to +₹5 crore, the percentage change is not meaningful, since the base is negative. Report the change in rupees (₹15 crore) and say “turned profitable”.
• From zero. The percentage change from zero is undefined. Use amounts.
• Both negative. A loss that narrows from −₹20 crore to −₹10 crore is an improvement of ₹10 crore. Calling it “−50%” is confusing, so many writers say “loss narrowed by 50%”.
• Very small bases. A change from 0.2 to 0.6 is 200% and is better described in absolute terms.

Share of a total versus change

Do not mix these. If a segment contributes 30% of revenue one year and 36% the next, its share rose by 6 percentage points. That is not the same as the segment growing 20% (6 ÷ 30), and it is also not the same as the segment’s revenue growing, since the total may have changed too. Say clearly which one you are describing.

A worked table

A fictional company reports, in ₹ crore, revenue of 500 last year and 560 this year; operating profit of 60 and 63; and profit after tax of 35 and 28.

• Revenue: +60, or +12.0%.
• Operating profit: +3, or +5.0%.
• PAT: −7, or −20.0%.
• Operating margin: from 12.0% to 11.25%, a fall of 0.75 percentage points.

In a report, this is best presented as a small table with columns for last year, this year, change in rupees and change in percent. Readers then see both scale and proportion at once.

Rounding

Decide how many decimals to show and keep it consistent. One decimal place is usually enough for percentages in business reporting. Round only at the end of a calculation, not at each step, or small errors accumulate. When percentages in a list should add to 100, note that rounding can make them add to 99.9 or 100.1, and say so if it matters.

Careful presentation of a simple calculation builds trust. Readers who can reproduce your figure from the numbers on the page are more likely to believe the rest of the report, and they are less likely to be misled by a number that was correct but poorly described.

For quick checks without building a sheet, a calculator built as a tool for percentage change between two figures lets you enter two numbers and see both the change and the working.

A report is only as clear as its denominators. State the base, the period and the unit every time, and most percentage mistakes disappear.