When an obligation falls due — which may precede the date it becomes overdue.
A due date is when an obligation arises. In everyday use it is a synonym for deadline, and in careful drafting it is not: an amount can be due on one date and only overdue after another, with a grace period between them.
The distinction matters where a penalty or an interest charge attaches. Interest may run from the due date even where enforcement waits for the end of the grace period, so 'not yet overdue' and 'not yet accruing interest' are different states.
As with most terms in this cluster, the instrument governs. Where a contract uses due date without defining it, the sensible reading is the strict one.
Often identical. Where they are not, the due date is when the obligation arises and the deadline is when failing it bites.
The grace period is the gap after the due date before consequences attach. It does not move the due date.
Maturity is when an instrument reaches the end of its term. A due date can arise many times before it.
See also deadline · grace period · maturity date · payment deadline
We hold this as not distinguished — the corpus records the operative date and its shift rule. See what we hold.