Seasonality index
A seasonality index expresses each month's typical level as a multiple of the annual average — 1.00 is average, 1.18 is 18% above. Built on an ingredient's price it tells you when to feature or retire a dish; built on your covers it tells you when to staff up.
Formula
Month index = Average value for that month ÷ Annual average
Three years of data is enough to be useful. One year is a guess with a decimal point on it.
Worked example · A produce item across a year
- Annual average price
- $2.40/lb
- July average
- $1.68/lb → index 0.70
- February average
- $3.55/lb → index 1.48
- Peak-to-trough swing
- 2.1×
A dish built on this item at a fixed price runs a fine margin in July and a bad one in February. Either rotate the dish seasonally or price it for the average and accept the swing knowingly.
What to do with the index once you have it
- Plan the menu against it. Feature an ingredient in its low months and retire it in its high ones. A seasonal menu isn't only a quality decision — it's the cheapest margin protection there is.
- Set your price against the average, not today. Pricing a dish off a trough-month cost guarantees a bad margin for half the year.
- Time your contracts. If a supplier offers a fixed price, you now know whether they're offering it above or below the annual average.
- Separate season from trend. A price up 30% in February isn't necessarily rising — check the index before treating it as price creep.
Related terms
Commodity index
A tracked measure of what a food commodity costs nationally — the benchmark that separates a market move from a vendor move.
Price creep
Small, frequent supplier price increases that individually look ignorable and collectively remove several points of margin a year.
Market price (MP)
A menu listing with no printed price, used for items whose cost moves faster than the menu can be reprinted.