A three-month structure measures curve shape rather than simply comparing two delivery months. This guide keeps the exchange, dated legs and historical-data boundary visible so the quoted relationship can be checked.
Three dated legs
A Minneapolis butterfly buys the first month, sells two of the middle month and buys the last month under the long-structure convention. The quoted value equals first price minus two times middle price plus last price. This is a difference between two neighboring calendar spreads, so it highlights the curvature of the term structure.
For example, July 2025 at 603.00 cents, September 2025 at 620.75 cents and December 2025 at 639.00 cents on 30 June yield 603.00 − 2×620.75 + 639.00 = +0.50 cent. The calculation is from a matched historical day, not a recommendation to trade it.
Why the middle leg is doubled
The −2 weight balances one unit of exposure in each wing in nominal bushels. It does not remove all risk: the middle delivery period can react differently to storage, local supply and liquidity. One butterfly contains four futures contract units gross, and execution as separate legs can expose the trader to temporary slippage.
Do not multiply the already weighted butterfly quote by four to estimate its dollar value. A one-cent change in the weighted expression corresponds to $50 per one 1:−2:1 structure, before costs, because each leg is quoted in cents for 5,000 bushels.
Backtest without shortcuts
Require a price for all three dated legs on the same day. If only two prices exist, the butterfly is absent; an interpolated middle leg changes the result. For each past season, preserve month and year offsets, then compare raw entry and exit butterfly values and inspect interim drawdown.
A smooth average butterfly curve can hide uneven years and thin overlaps. Report the number of matched days and years next to the figure, and do not publish a current 2026 butterfly from a dataset whose Minneapolis leg prices end in 2025.
See the dated contracts behind the formula
Explore matched historical Minneapolis prices, individual years and the selected date window. The dataset has no verified current MGE spread.
Open MGE Historical Research →Primary sources
Exchange and USDA sources establish product definitions and context. Recheck the current rules and dates before using a contract.
Continue this series
Educational historical research, not investment advice. Futures and multi-leg spreads involve substantial loss, execution and delivery risk. Historical results do not guarantee future outcomes. Imported Minneapolis prices stop on 24 October 2025; current quotes and margin must be verified independently.