A perpetual swap has no expiry, so an exchange bolts on a funding payment to keep it near spot. This lab tests a single hypothesis: that a perp is — in the financial sense — just an 8-hour future whose position is automatically rolled every interval, where funding is the roll's carry. Some rolls pay you, some charge you; that is funding.
How Binance, BitMEX, OKX, Bybit, Hyperliquid and dYdX each compute funding — the shared F = P + clamp(I − P, ±cap) template, mark-vs-index pricing, and where the venues diverge (8h vs hourly, mark vs oracle notional, caps).
Kalshi's "no-expiration" futures with 8h funding, and Coinbase's US Perpetual-Style Futures — a 5-year long-dated contract with hourly-accruing funding, DCO-cleared. The regulated versions are literally auto-rolling cleared futures.
Expiry cycles, cost-of-carry F = S·e^((r−q)T), cash-and-carry arbitrage, convergence, daily mark-to-market, and the calendar-spread roll — the baseline the perp reinvents.
The derivation: funding = basis-per-interval = carry-per-interval, matched to the academic no-arbitrage result — plus the five places the analogy leaks (dead-band, mark notional, compounding, accounting, reopen premium).
The interactive calculator runs a virtual perp and a virtual auto-rolling future on the same seeded price path and overlays their equity curves. Pick a funding model — fair carry, Binance/BitMEX clamp, Deribit dead-band, Hyperliquid hourly, or a constant rate — and watch the two curves either coincide exactly or split apart by the tracking gap.
Fair-carry funding ⇒ perp and future equity overlap to machine precision, path-by-path.
Set the future to replicate funding and any perp — even a clamped one — is matched by construction.
A rich premium or a constant rate makes funding depart from carry — the gap you see is exactly the analogy's leak.