Demurrage and Detention Are Two Clocks

Split by whatever actually changes the days — the port, the buyer, the season — rather than by trade lane out of habit. Days in the terminal run from discharge to the box leaving the gate; days before the empty goes back run from gate-out to empty return, and that second one is where a factory's own destuffing and container-return discipline shows up rather than anything a shipping line did. The two free-day columns come from two different contracts and are genuinely often different; entering the same number in both because that is what everyone says is the specific mistake this sheet exists to correct.