Annualized yield

The premium as a return on the collateral, scaled to a yearly rate over the days the option is held — so a 30-day put and a 90-day call compare on the same footing. A 2% premium over 30 days is roughly a 24%/yr run-rate. Treat it as a comparison aid, not an expectation: a 7-day option paying 0.5% annualizes to 26%, a rate nobody collects 52 times running.