Theta

Theta is negative for long options and positive for short options: every day that passes, all else equal, a long option is worth a little less and a short option owes a little less. Decay isn't linear — it accelerates sharply in the final few sessions before a weekly expiry, which is exactly why holding long premium into expiry week is one of the most common ways a directionally-right trade still loses money.

Example: a NIFTY ATM call at ₹180 with five sessions left might lose only ₹15-20 a day early in the week — then ₹40-50 in the final session alone, on an unchanged spot. Same option, same strike, decaying faster purely because there's less runway left.