Definition
Cobweb Model
The cobweb model explains recurring price and output cycles in markets such as Indian agriculture, where supply responds to prices with a time lag because producers plan output on the basis of last season's prices.
Why do onion and tomato prices in India swing from giveaway-cheap to painfully expensive almost every year? The cobweb model is the classic economics answer. It describes markets where farmers must decide *how much to plant* long before they know the price they will actually get, so they plan using last season's price as their guide.
How the cycle spins
Say tomato prices crash at harvest. Disheartened growers plant far less next season, supply shrinks, and prices spike. Those high prices then lure everyone back, output floods the mandis, and prices collapse again. Because supply reacts to price with a one-season lag, the market chases its own tail, tracing a cobweb-shaped path on a supply-demand chart. This is a textbook case of adaptive expectations producing instability rather than a calm equilibrium.
India sees it vividly in the Tomato-Onion-Potato (TOP) basket. A glut can push onion farm-gate prices to a few rupees a kilo, while a shortage sends retail past ₹80. The same logic appears in pulses, where dal price spikes one year trigger bumper sowing and a price slump the next, forcing the government to step in with buffer stocks and import-export tinkering.
Why it matters for investors
Whether the cobweb converges to stability or explodes outward depends on how steeply supply and demand respond to price. The bigger lesson is about food inflation, which the RBI watches closely because volatile vegetable prices repeatedly knock CPI above its 4% target and complicate rate decisions.
For mutual fund investors, the cobweb model is a reminder that agri-linked and commodity themes are inherently cyclical. The fix is not to predict each turn but to recognise the pattern. Government tools, better cold-chain storage, futures markets on exchanges like NCDEX, and reliable price-forecast data all aim to break the cobweb by helping farmers plan on expected future prices rather than yesterday's. Until information improves, the cycle persists, and the periodic vegetable-price headlines that rattle household budgets are not random shocks but the predictable rhythm of a lagged-supply market.
Plain-English explainer from The Dispatch Investors Encyclopedia. General information, not financial advice.