A calendar can be reused when the year starts on the same weekday and matches its leap-year status. 2026 begins on a Thursday and is a common year, so its calendar repeats exactly in 2037 — 11 years later — and again in 2043, 2054, 2065, 2071.
A year’s calendar is fully determined by two things: the weekday its first day falls on, and whether it is a leap year. Any two years that match on both are identical day for day, which means an old wall calendar becomes usable again.
Common years usually repeat after 6, 11 or 5 years; leap years repeat every 28 years while the pattern holds.