Time after a due date before consequences attach — and it is not an extension.
A grace period is a span after a due date during which an obligation can still be met without the usual consequence. It is common in tax, insurance and lending.
It is not an extension of the deadline, and treating it as one is the standard error. Interest frequently accrues from the original due date through the grace period; what is suspended is the penalty, not the clock. A payment made inside grace is late and forgiven, not on time.
Grace periods are also not universal within a jurisdiction. One tax may carry one and the next may not, which makes them a poor thing to assume.
The grace period runs from the due date. It does not move it, and interest may keep running through it.
A grace period softens the consequence of missing a deadline. It does not create a later one.
See also due date · deadline · payment deadline · statutory deadline
We hold this as not held — grace is a property of the obligation, not of the calendar. See what we hold.