Three TSLA calls bought today, stock held flat at $420. The scale never moves, so you can watch each one bleed away as time runs out. Grab the vertical line and slide it left or right to any number of days remaining; the readout shows what each call is worth on that day. Lock a variable to hold it still and isolate one effect.
At day 0 the ATM call is worth nothing- all of that is time value waiting to evaporate.
Plain English
Three things to know about time decay:
Decay is not steady, it accelerates. In practice it is slow far from expiration and speeds up hard in the final weeks.
The strikes decay differently. The at-the-money option bleeds fastest near the end, the in-the-money one keeps its intrinsic floor, and the out-of-the-money one fades toward zero.
So give yourself room. A short-dated option needs you to be right fast; generally speaking, more time is the cheaper mistake.
Taxes are not shown here. Options and the underlying stock are taxed differently, and it depends on your holding period and account type. None of this is tax advice.