How theta decay actually works, day by day

Options time decay, with the actual numbers

Published July 16, 2026 · Updated July 17, 2026

Theta decay is the value an option loses each day just from time passing, and the pace is anything but steady. A typical two-month option bleeds around 1% of its value per day, but that same option in its final week loses 17% or more of what's left every single day.

The table below makes the curve concrete: one option, tracked from 60 days to expiry with the stock pinned in place, so the only thing eating it is the calendar. Every number is computed with the Black-Scholes model, the same math the calculator runs. You can also watch the decay on your own position:

What theta actually charges you for

An option's price has two parts. Intrinsic value is what exercising would be worth right now. Extrinsic value is everything above that, and it's payment for the chance of a bigger move before expiry. A $105 call on a $100 stock has no intrinsic value at all; its entire price is a bet that the stock reaches new ground before the clock runs out.

Every day that passes removes one of the days in which that move could happen. The chance shrinks, so the price of the chance shrinks with it. Theta is simply the per-day size of that markdown. Nobody is charging you a fee; the thing you own is a claim on future movement, and its future keeps getting shorter. If the stock never moves, the markdown continues until the option expires worthless, which is why an option can bleed to zero while the stock does nothing wrong.

The acceleration curve: one option, 60 days to zero

Say the stock trades at $100 and you're watching the $105 call at 45% implied volatility. Here's that exact option repriced at eight checkpoints on the way to expiry, holding the stock at $100 and IV at 45% the whole way so time is the only force in play. "Daily decay" is the day's theta measured against what the option is still worth:

Values computed with the Black-Scholes model at a 4.5% risk-free rate. It's the same math the calculator runs. *At 1 day the model's quoted daily bill exceeds the option's entire remaining value; an option can't lose more than it has, it simply expires.

Read it top to bottom and the shape of the curve jumps out:

• The early days are cheap. The first 15 days, a quarter of the option's entire life, cost $1.03, about 19% of its value. At this stage theta is a slow drip: with 60 days left, losing one of them barely changes the odds of a move.
• Half the value is gone by 24 days out. Not at the halfway mark of the calendar. At 30 days to expiry the option still holds about 60% of its starting value; the crossing point comes days later and the slide is steepening.
• The last two weeks are the cliff. Between 14 and 7 days the option loses more than half of what remains. The final week vaporizes the rest: the $0.81 left at 7 days, about 15% of the starting value, goes to zero in seven days.
• The daily bill more than doubles as the option shrinks. At 3 days out, theta is −$0.139 per day, more than twice the −$0.065 charged at 60 days, on an option worth one twentieth as much. Late-stage options look cheap precisely when their per-day cost of ownership is at its worst.

The mechanism is the same one from the section above: with 60 days left, losing one barely dents the odds of reaching $105. With 3 days left, nearly all the remaining chance lives in each individual day, so each one that passes takes a huge bite.

Where the "30 to 45 DTE sweet spot" idea comes from

You'll often hear that 30 to 45 days to expiry is the sweet spot for option sellers, who collect theta rather than pay it. The table shows the logic. In that window the daily decay rate has picked up meaningfully, from 1.2% of the option's value per day at 60 days to 1.6% at 45 and 2.7% at 30, but the position is still weeks away from the final stretch, where a single adverse move can erase a month of collected decay overnight.

The same table read from the buyer's side explains the companion heuristic of exiting before roughly 21 days: past that point the per-day bill climbs from 4% of remaining value toward 7%, then 17%, and holding through it means the stock must move fast just to keep the position flat. Neither number is magic. The curve is smooth, nothing special happens on day 45 or day 21, and faster decay is always paired with its own risks, because the fat late-stage theta a seller collects is compensation for the fat gamma risk they carry. The numbers tell you what each week of the calendar costs; whether any given trade is worth it is a judgment this site doesn't make for you.

How to see the decay on your own position

The projection board on the calculator puts dates across the top and stock prices down the side, repricing your exact contract in every cell. Read across any row and you're watching pure time decay: the same stock price, marched forward through the calendar, exactly like the table above but for your own strike, expiry, and IV. The position panel's "Theta /day" readout is today's bill, and the row shows you how that bill compounds and accelerates from here to expiry.

Why isn't my option moving?

A close cousin of time decay: sometimes the stock moves and your option barely does. The usual reason is not theta but low delta. Delta is how much the option moves per $1 move in the stock, and a far out-of-the-money option only captures a small slice of each dollar. Here are four 30-day calls on a $100 stock at 45% implied volatility, from at the money to deep out of the money:

Values computed with the Black-Scholes model at a 4.5% risk-free rate. Same math the calculator runs.

• Far out of the money, the option is sluggish by design. The $115 call moves only about $0.16 for a $1 stock move. The stock has to travel a long way, or get closer to the strike, before the option wakes up.
• Wide spreads hide small moves. On thin options the bid-ask spread can be wider than a real change in value. Watch the mid-price, not the last trade.
• Volatility and time can cancel a correct call. If implied volatility falls, or theta eats a small favorable move, the option can look frozen even though the stock rose. This is common right after earnings.

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