Question Handling Calendar Edge Cases in Date-Difference Calculations for Web Applications

[Savannah_Tepper]

I've been exploring date-handling logic in web applications and noticed that calculating the difference between two dates is not always as straightforward as it seems.

I'm particularly interested in how developers handle calendar-based calculations when building applications that need accurate results across different months and years.

For example, consider a web application that calculates the duration between a user's starting date and a selected end date. It might need to display the total number of days, completed months, years, and even upcoming milestone dates.

Which provides exactly this type of functionality for relationship anniversaries and milestones. It calculates elapsed time, identifies dates such as the 100th, 500th, and 1,000th day, and accounts for leap years and varying month lengths.

Looking at this use case raises some interesting implementation questions, especially for developers working with Progress applications and database-backed systems.

Some edge cases worth considering:

1. Leap-year handling: How should February 29 be handled when calculating anniversaries in non-leap years?
2. Inclusive counting: If the starting date is day one, how should the 100th-day milestone be calculated compared with 100 full elapsed days?
3. Month boundaries: Should completed months be calculated using calendar arithmetic rather than approximating every month as 30 days?
4. Date storage: Is it better to store date-only values separately from timestamps to avoid unexpected time zone conversions?
5. Validation: What test cases would you use to verify date calculations across month boundaries and leap years?

For those working with Open Edge ABL, SQL-92, or other backend technologies, how do you generally approach these scenarios?

I'd be particularly interested in practical examples of reliable date arithmetic and reusable date-calculation functions in production applications.