What actually happens on the day a fund rolls?
Contracts expire; exposure does not have to. Anyone holding a commodity position for longer than one contract's life must roll — close the expiring contract and open a later one. The Futures & Forwards course establishes that. What it leaves open is the execution, and a misconception about the execution that survives almost every explanation of it.
The roll is one trade, not two
A roll is not "sell the front, then hope to buy the next at a good price." Exchanges list calendar spreads as instruments in their own right, with their own order books and their own quotes.
So a roll is submitted as a single spread order — sell M1 and buy M2 simultaneously — quoted as a difference, for example "M1/M2 at −1.50". Both legs fill together at that difference or neither fills. There is no leg risk, no slippage between the two halves, and the price you care about is the spread, not either outright price.
This is why professionals discuss the roll in terms of the spread level and never in terms of where the front month happened to be trading that morning.
Rolls are scheduled, and the schedule is public
Large systematic holders — index trackers, exchange-traded products — do not roll everything in one print. They roll across a published multi-day window, moving a fraction of the position each day. The methodology is disclosed in advance in the prospectus or index rulebook.
The reason is defensive. A single-day roll of a very large position is a known quantity of one-sided flow arriving at a known time, and the spread would move against it. Spreading the flow across several days reduces, without eliminating, how much the roll costs itself. More on that in the fourth lesson of this unit.
The misconception: the roll does not cost you anything on roll day
This is the part that gets stated backwards constantly.
Take a contangoed market. On roll day, spot is $78.00, the expiring front contract has converged to $78.00, and the next contract trades at $79.50.
- You sell M1 at $78.00 — the position you held is closed at the market.
- You buy M2 at $79.50 — a new position is opened at the market.
- Cash profit or loss booked today: zero. You transacted at prevailing prices on both legs.
Nothing was lost on roll day. What happened is that your exposure has been re-based to a higher entry price in a market whose spot price is still $78.00.
Now let a month pass with spot completely unchanged. Your M2 contract is now the front month, and convergence does what convergence must: it pulls the contract to $78.00. Your position, entered at $79.50, is marked at $78.00.
−$1.50 a barrel = −$1,500 on a 1,000-barrel contract, arriving as a month of ordinary daily settlement debits.
So: the roll cost is committed to on roll day and paid by convergence over the following month. Anyone looking for the loss in the roll-day statement will not find it, and will conclude the cost is a myth.
The same mechanism is inside your data
A continuous front-month price series — the kind published by many data vendors — is built by rolling too, and vendors differ in how they stitch it:
- Unadjusted. Successive contracts joined end to end. The series jumps at every roll date by the size of the spread. Those jumps are artefacts, not price moves.
- Back-adjusted. History is shifted so the joins are smooth. The series is continuous, but the historical levels are no longer the prices that actually traded.
Neither is wrong; both are wrong if you forget which one you have. A return computed across a roll date in an unadjusted series is not a return anybody could have earned.
A third possibility is that your series has no joins at all, because it was never a futures series. A spot assessment at a delivery point, such as the monthly WTI-at-Cushing price used earlier in this course, carries no roll and therefore no roll artefacts, and also no roll yield. The joins live in the dated futures contracts, one price series per contract month, which you stitch yourself or not at all.
Try it now
- A year of crude as daily candles is below. Scan it for a join: a gap between one session and the next too large to be a plausible overnight move in a market that traded all night. A continuous front-month series carries those joins wherever the stitching happened; a spot assessment cannot have them at all.
- Measure across one candidate gap and write the size down, then check the exchange's settlement data for those two days. Two separate contracts, or one contract that moved? The answer decides whether you found a roll or a price.
- State the roll rule in one sentence: the roll books nothing today and everything over the following month.