why do we have a leap year

Leap years exist to keep our calendar aligned with Earth’s orbit around the Sun. A solar year is about 365.2422 days, not exactly 365. Over time, those extra hours would accumulate if left uncorrected, causing the calendar to drift relative to the seasons. By adding an extra day (February 29) every four years, we compensate for roughly 0.2422 days per year, keeping seasons in the same months and days over long periods. To fine‑tune this further, century years are not leap years unless divisible by 400, which brings the average year length to about 365.2425 days, even closer to the solar year. If you’d like, I can tailor this explanation to a specific audience (students, curious adults, or a quick one‑sentence summary).