Perpetuals: The Contract That Never Expires

A perpetual lets you bet on a price with leverage and no expiry — kept honest by a small fee that flips direction to track spot.

Crypto & Tokenization · Lesson 27 · 10 min read

The single most-traded thing in crypto isn’t Bitcoin the coin — it’s a perpetual future on Bitcoin: a contract to bet on the price, with borrowed size, that never expires. Two puzzles make it strange. First, if it’s just a contract and not the real coin, what stops its price drifting away from the actual coin’s price forever? Second, how can a small move wipe out a trader in minutes? One clever fee answers the first; leverage plus last lesson’s liquidation answers the second. Hold the question: how do you tether a paper bet to a real price with no expiry date?

A perpetual is a leveraged bet with no expiry

A normal future is an agreement to settle at a set price on a set date (you met the farmer’s version in a finance analogy). A perpetual strips out the date — it never expires, so you can hold a position as long as you like. You post a little margin and control a larger position: that’s leverage. At 10× leverage, $100 controls $1,000 of exposure — so a 1% move in the coin is a 10% swing in your money. You never own the coin; you’re long or short its price. Great for hedging, brutal as a gamble — same double edge you’ll meet again in the finance track.

The funding rate keeps it tethered to spot

Here’s the elegant part. With no expiry to force the contract price back to reality, exchanges use a funding rate: a small periodic payment between longs and shorts. When the perpetual trades above the real (spot) price — too many longs — longs pay shorts, which nudges people to stop going long and pulls the price down. When it trades below spot, shorts pay longs. The payment flips whichever way is needed, so traders are constantly, gently paid to push the contract back toward the real price. No referee sets it — the imbalance does. That’s why you can check the funding rate to read who’s crowded.

Funding doing its job:
• Everyone’s bullish, so the BTC perp trades at $70,500 while spot is $70,000 — a 0.7% premium.
• Funding turns positive: longs pay shorts a small fee every few hours.
• Paying to stay long gets annoying; some longs close, new shorts appear, and the perp drifts back toward $70,000. The fee didn’t force anything — it just made the crowded side pay to stay crowded.

Leverage + mark price = fast liquidation

Leverage is why perpetuals are dangerous. Your margin is a thin cushion; at 10× a ~10% adverse move wipes it out and you’re liquidated exactly like the over-collateralized borrower from last lesson — the position is force-closed to protect the exchange. To stop nasty tricks, liquidation is judged against a mark price (an average of real prices) rather than the perp’s own possibly-manipulated last trade. The honest summary: perpetuals let a real business hedge and let a gambler get liquidated fast — the instrument is neutral, the leverage is the risk. This is education on how the tool works, not advice to touch it.

A 10× long getting liquidated:
1. You post $500 margin and open a $5,000 long on ETH (10× leverage).
2. ETH falls 8%: your $5,000 exposure loses $400 — most of your $500 cushion.
3. As the mark price crosses your liquidation level, the exchange force-closes the position to avoid a loss to itself.
4. You’re out ~your whole margin from an 8% move, because 10× turned it into ~80%. The coin barely moved; the leverage did the damage.