Theta is how much an option's price falls per day, all else equal — and for the premium seller it's the paycheck. It only ever eats extrinsic value, the time-and-possibility premium: each quiet day moves real dollars from the buyer's ledger to the seller's. A 30-day at-the-money put on a $100 stock at 30% IV starts near $3.26 and melts about $5 a day per contract; if the stock never moves, the whole $326 lands in the seller's barn.
The decay curve's shape is the seller's edge. ATM extrinsic value scales with the square root of time, so decay accelerates into expiry — the last 30 days melt more than the first 30, and the final week melts fastest. Far-OTM options do the opposite: their small premium bleeds out early and flattens, because the market writes off the long shot with days to go.
That geometry is why sellers cluster in the 30–45-day window. And the 'free weekend theta' pitch mostly fails: market makers shade implied vol down into Friday's close, pricing the weekend melt before it happens.
The catch is the theta/gamma coin: the daily income is compensation for being short gamma — exposed to sharp moves — and it's richest exactly where gamma is most explosive, at the money near expiry. The interactive decay curve lets you slide days elapsed, switch ATM / 5% OTM / 10% OTM strikes, and watch theta per day, value left, and percent melted in real time.
Educational, not investment advice.