Bitcoin Futures ETF Contango and Decay Explained

A bitcoin futures ETF such as ProShares' BITO never owns a bitcoin. It owns futures contracts - agreements to settle against bitcoin's price on a set date - and those contracts expire. So the fund sells the expiring one and buys a later one, every month, for ever. Later contracts normally cost more than nearer ones, that gap is called contango, and paying it twelve times a year is the decay people notice when they compare the fund with bitcoin itself.

What is contango?

Think of plane tickets. A seat on next month's flight usually costs more than one on tomorrow's, because part of the price is the certainty of having it locked in. Futures behave the same way: the contract settling in December typically trades a little above the one settling in November. When that is true, the market is said to be in contango. When it flips, and nearer contracts cost more than later ones, the word is backwardation - the rarer state for bitcoin.

How the gap turns into decay

Every month the fund is a forced seller of the cheaper contract and a forced buyer of the dearer one. Each roll shaves a sliver off the return, and the slivers compound: a few percent a year when the curve is flat, considerably more when traders are excited and it steepens. Nothing is being stolen and nothing is mismanaged. The fund is doing exactly what its documents say. It simply carries a cost that a spot fund - one that buys real coins and leaves them with a custodian, as BlackRock's IBIT does - never pays.

Why the decay is invisible day to day

Over a week, BITO moves almost exactly like bitcoin, which is why it looks perfectly fine on a short chart. The drift only shows up over months and years, and it runs in one direction. That makes a futures ETF a defensible vehicle for a short trade and a poor one for a long hold - close to the opposite of how most people actually use a fund they have bought.

Before buying any bitcoin fund, find the one line on its fact sheet that says what it holds. "Bitcoin futures" and "bitcoin" are different products with different arithmetic, and the fee is the smaller half of the difference. The two structures sit side by side in bitcoin spot ETF vs futures ETF, and the bill is itemised in BITO's expense ratio and roll cost.