Why does an option lose value even when nothing happens?

You buy a call. The stock closes flat for a week. Your position is down. Nothing went wrong — the instrument did exactly what it was built to do. Options are the only common asset with a countdown running inside the price, and this lesson makes that countdown concrete.

Time value drains, and not linearly

Take an at-the-money call worth $4.00 with 90 days to expiry. It is ATM, so all $4.00 is time value. Hold the stock price perfectly still and the price of that option, as a rough but honest approximation, scales with the square root of the time remaining:

Two things jump out. Halving the time from 90 days to 45 does not halve the value — it removes only about 29%. And the last few days are a cliff.

The acceleration, in dollars per day

Look at the rate rather than the level:

• From day 90 to day 89, the option loses about $0.02.
• From day 2 to day 1, it loses about $0.18.

Same contract, same stock, roughly eight times faster decay at the end. This is the single most counterintuitive fact about options and the reason experienced desks talk about the last two weeks of an option's life as a different regime entirely.

The Greek that measures this is theta, quoted as a negative dollar amount per day. A $4.00 option with theta of −$0.02 is bleeding $2 per contract per day, every day, including weekends and holidays, whether the market is open or not.

Why longer-dated options are not proportionally dearer

Flip the table around and it becomes a buying observation. A 30-day option costs $2.31; a 90-day option costs $4.00. Three times the time for 1.73 times the price — because √3 ≈ 1.73. Time is priced with diminishing returns.

The trap this creates

Time decay produces the most demoralising experience in options: being right and losing anyway. The stock does rise — in month four. Your three-month call expired worthless in month three. You had the correct view of the company and the wrong view of the calendar, and the instrument does not award partial credit.

Decay runs against the buyer and toward the writer, every day, mechanically. State that as a fact about the contract, and stop there — the previous unit already showed what the writer is accepting in exchange for collecting it.

In the data

Apple's chain is below, in the EODHD Terminal, one expiry date at a time.

Open AAPL.US — options in the EODHD Terminal

"Days to expiry" is almost always counted in calendar days, weekends and holidays included: from 12 August 2025 to 17 December 2027 is 857 days. Decay is usually reasoned about in trading sessions, and a calendar count does not know about those. A "30-day" contract holds roughly three weeks of trading, and any per-day cost divided out of the calendar count is diluted to match.

Try it now

1. Pick one strike near the current price in the chain above and follow it across expiries: roughly one month, three months and one year out. For each, note the call's premium (midpoint of Bid and Ask) and count the days from today to that expiry date.

2. Divide each premium by its days to expiry. Note that the cost per day of life is far higher for the short-dated contract — you are paying a premium for urgency.

3. Check whether the 12-month premium is anywhere near 12 times the 1-month premium. It will not be. Write down the ratio you actually find, and compare it with √12 ≈ 3.5.