A dip on schedule is not a trend.
Vegetable prices keep a calendar: the winter glut, the summer climb, the occasional monsoon spike. How to tell the season from the trend, and why winter always looks like relief.
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 principlesVegetable prices keep a calendar. Every winter the new harvest reaches the mandis, supply gluts, and the food price level dips; every summer it climbs back. The rhythm repeats with such regularity that you can nearly read the month off the shape of the chart.
None of this is a trend. A winter dip means winter arrived, not that inflation is beaten, and a monsoon spike means the rains failed somewhere, not that prices are out of control. The trap is that both feel like news. Every winter the level falls, and every winter someone calls it a turning point.
The calendar, drawn ten times
Food index level, monthlyBelow is the food price level for a full decade, with the four months from November to February shaded every year. The pattern needs no model and no statistics: the line sags inside the grey bands and climbs outside them.
The same dip, every winter: the calendar is the pattern
The grey bands are November to February, every year for a decade. Watch the line inside them: it ends – of the shaded windows lower than it began, as the winter harvest comes in. Then watch what it does each summer: it climbs back, and further. The wobble is seasonal; the climb is the trend.
Across the whole decade the level rose –. The winter dips subtracted nothing from that total; they only delayed it. A seasonal fall is a pause with a date on it, and the date is the tell.
The deepest dip of the decade followed the sharpest spike. The food level entered November 2024 at – and left February 2025 at –, a fall of –. Commentators called it victory over inflation. It was winter.
The line had done the same thing, on the same schedule, eight times before. Relief that arrives with the harvest leaves with the summer, and it did.
Why year-on-year exists
Cancelling the calendarThere is a way to cancel the calendar: never compare a month with its neighbour. Compare it with itself, one year back. December against December carries the same weather, the same festivals and the same harvest on both sides of the ratio, so the seasonal wobble divides out. What remains is closer to real change.
This is why the headline inflation rate is always a year-on-year figure, and why the month-on-month change, for all its speed, is mostly weather. The companion entry, Year-on-year, month-on-month, takes the two measures apart. The short version: one is slow and honest; the other is fast and mostly noise.
How to misread this concept
- i.
“Prices fell this winter, so inflation is beaten.”
Prices fall most winters; that is what winter does to food. Beaten inflation would show up in the year-on-year rate, which compares this winter with the last one. A seasonal dip and a falling rate are different animals, and only one of them is news.
- ii.
“A festival-month spike is a crisis.”
No. Demand keeps a calendar too, and if the same spike arrives every festival season and unwinds right after, it is a season, not a crisis. Check the same month a year back before reaching for the word.
- iii.
“Seasonality means the data is wrong.”
The opposite. Seasonality means the data is honest enough to show the weather. The error is in the reading, not the recording: a pattern you can predict is not noise, it is information you have not used yet.