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How much longer was the Julian calendar year than the tropical year?

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Kalendarium (“Calendar”) by Regiomontanus — calendar First complete printed title page for the *Kalendarium* (“Calendar”) by Regiomontanus, 1476.

The Julian calendar year was established with a length of 365.25 days. In contrast, the mean length of the tropical year is approximately 365 days, 5 hours, 48 minutes, and 45.5 seconds.1

By overestimating the length of the year by 11 minutes and 14 seconds, the Julian calendar was longer than the tropical year by that amount. This cumulative discrepancy caused the dates of the seasons to shift by about 10 days by the mid-1500s, eventually leading to the adoption of the Gregorian calendar to restore alignment with the solar year.1