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Growth rates are easy to compute and easy to be fooled by. The most common reason is the base effect: the size of the starting number changes what a percentage means.
A simple illustration
Consider a fictional company, Ganga Pumps, over three years. Annual profit in ₹ crore:
- Year 1: 10
- Year 2: 20
- Year 3: 24
Profit grew 100% in Year 2 and only 20% in Year 3. A headline would read “growth slows sharply”. But in rupees, the profit increase was ₹10 crore in Year 2 and ₹4 crore in Year 3. Both years added to profit; the second simply started from a larger base, so the same rupee gain gives a smaller percentage.
The reverse: low bases flatter, high bases punish
Suppose Year 4 profit falls to ₹12 crore. That is a 50% fall. To get back to ₹24 crore in Year 5, profit needs to rise by 100%. Percentages are not symmetrical, which is why a recovery that looks dramatic may just be a return to where things were. The arithmetic is set out in an explainer on why a 50% fall needs a 100% rise to recover.
The base effect in the news
You will see it whenever a period is compared with an unusually weak or strong one. Economies reopening after a disruption show very high growth rates because the previous period was depressed. A month with a one-time festival shift looks strong against a month without it. A year after that, the high growth fades, and the same underlying performance gets labelled “slowdown”.
How to guard against it
- Look at the rupee change next to the percentage. If a company adds ₹4 crore to a ₹20 crore base, say so.
- Check what the comparison period looked like. Was it unusually good or bad?
- Use a longer window. A two- or three-year growth rate (CAGR) smooths out one odd base.
- Compare like periods. Use the same quarter last year for seasonal businesses.
One more example
A business moves from ₹100 crore to ₹110 crore, then ₹121 crore, then ₹133 crore. The growth is a steady 10% a year. A neighbouring business goes ₹100, ₹60, ₹110, ₹121. Its latest growth is 10%, and its Year 3 growth is an eye-catching 83%. Both reach similar places, but the stories are very different. Percentages alone cannot show it.
The base effect in other settings
Economic output. Suppose a fictional economy’s output is 100 in one year, falls 10% to 90 in a disrupted year, and then rises 10% to 99 the next. Growth is “10%”, but output of 99 is still 1% below where it started. Two years on, the economy has not regained its earlier level. Headlines about the growth rate alone can leave the impression that the loss has been recovered.
Prices. If a price index rose sharply in one year, the following year’s inflation rate can fall even when prices keep rising. The rate has dropped, but the price level is still higher than before. Lower inflation is not falling prices.
Monthly data. Compare one month with the same month last year and watch for shifts: a festival that fell in one month last year and another this year can make both months look strange. Longer windows help.
Practical rules
- Ask what the comparison period looked like. Was it unusually weak, unusually strong, or normal?
- Use two comparisons where you can: the previous year and the year before that. If both point the same way, the story is more reliable.
- Convert to levels. Write the actual values over a few periods, rather than only the percentages.
- When growth rates are extreme, either high or low, check the base before reading anything into them.
A short exercise
A fictional company has profit of ₹8 crore, then ₹2 crore, then ₹6 crore. The growth in the last year is 200%. Is this a strong year? Profit is still below the ₹8 crore of two years ago. The percentages describe a recovery from a bad year, not a record. Now compute the two-year CAGR from ₹8 crore to ₹6 crore: (6 ÷ 8)^(1/2) − 1 = −13.4%. Over the longer window, profit has fallen.
Neither number is wrong. The 200% is the answer to “how much did profit change in the last year?” and −13.4% is the answer to “what is the yearly rate over two years?” The skill is choosing the question that fits what you want to know, and saying which one you answered.
The base effect shows up in almost every set of numbers that change over time, so it is worth making “growth from what?” an automatic question.
The base effect is not a trick played by anyone; it is arithmetic. Knowing it exists lets you ask the right follow-up question each time. For worked examples in the context of company results, see how the base effect changes a growth figure.
Next time you see a very large or very small growth figure, ask one thing first: growth from what?
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