Why onions move inflation more than rent.
The CPI is not a list of prices. It is a budget, in which each item counts in proportion to what households actually spend on it, and the spending shares come from a survey taken in 2011–12.
The charts on this page draw the consumer price index on its 2012 base, the series that ran to December 2025. From January 2026 the NSO publishes the index on a new base, 2024 = 100. The idea on this page works the same on either ruler; the latest figures are in the Consumer prices guide.
The word, defined
First principlesAsk how the national inflation number is built and most people picture a list: three hundred items, each checked monthly, each counting once. The picture is wrong in one decisive way. The basket is not a list but a budget. Rice and rent and bus fares do not get one vote each; they get votes in proportion to the money households actually spend on them.
Those proportions are the weights. They come from the 2011–12 Consumer Expenditure Survey, a nationwide canvass of what households bought, and they stayed frozen into the index for as long as the 2012 base ran, to December 2025. Food and beverages carry 45.86 of every 100 points in the combined index. Housing carries 10.07. Pan, tobacco and intoxicants carry 2.38.
This is why onions can move the national number and your rent barely registers. Vegetables sit inside the largest group in the budget, so a bad crop can lift the whole index for months. Housing, the expense urban families feel most keenly, carries less than a quarter of food's weight.
What the survey found
Weights, per cent, CES 2011–12Six groups, frozen from the 2011–12 Consumer Expenditure Survey. Food alone is nearly half the index: the reason a bad onion crop can move the national inflation rate while rents, for most urban households the heaviest bill, move it so little.
The budget, drawn to scale
Points of 100One hundred points of spending, divided six ways: food speaks loudest
Each bar is a group's share of the national budget, out of 100 points. Read them as paise in a rupee: 46 go to food, 28 to the services and odds-and-ends of the miscellaneous group, 10 to housing. The length of a bar is how loudly that group speaks in the national number.
Two implications follow. A price shock in a long bar moves the index even if everything else is calm. And a price shock in a short bar, however painful for the households it hits, barely reaches the average.
In late 2019 onion prices spiked after unseasonal rain ruined the crop, and food inflation climbed to – by December. Because food carries nearly half the index, the headline followed it to –, well above the 4 per cent target the RBI is bound to defend.
A single vegetable, weighted by a billion kitchens, moved the number that Indian monetary policy is legally organised around. That is what a weight of 45.86 means in practice.
Why your inflation is not the national inflation
A worked example, Dec 2025The national number is the average budget made flesh, and no household is average. Take a family that spends 60 per cent of its budget on food, common enough in rural India, and put the remaining 40 per cent into everything else at the national rates. In December 2025 their index rose – while the national print read –: same country, same month, a gap of –.
A year earlier the arithmetic ran the other way. In December 2024 the same family's index rose – against a national print of –, because food, their heaviest bill, was spiking while services were calm. Their inflation ran hotter than the headline in 2024 and cooler in 2025. Both years, it was theirs.
This is not a flaw in the index. An average must choose a budget, and any budget it chooses will belong to no one. The honest use of the national number is as a common yardstick, not as a description of your kitchen.
How to misread this concept
- i.
“Every item counts equally.”
No. Food carries 45.86 of every 100 points; pan, tobacco and intoxicants carry 2.38. A 10 per cent rise in food prices moves the index about nineteen times as much as the same rise in pan prices. An index in which every item counted once would be a different, and stranger, measure.
- ii.
“My inflation is the national inflation.”
Only if your budget is the 2011–12 average, and no one's is. A family spending 60 per cent on food lived at – in a month when the national print read –. The index describes the average household. You live in a specific one.
- iii.
“The weights are fixed forever.”
They are fixed until they are not. The 2011-12 survey governed every print on the 2012 base. From January 2026 the 2024 base replaced it with a newer budget, as earlier revisions did: the weights shifted, and the same prices now print a slightly different index.