The adoption of the Gregorian calendar occurred slowly over a period of centuries, and despite many proposals to further reform the calendar, the Gregorian Calendar still prevails as the most commonly used dating system worldwide. How to understand a difference between two dates? Ask a new question Source code dCode retains ownership of the source code of the script Difference between 2 Dates online. How to calculate an age in number of days? He also added the intercalation of a leap day every fourth year, all in an attempt to further synchronize the Roman calendar with the solar year. By , this resulted in a difference of 10 days from what was expected.