Date math sounds simple until you're actually doing it - months have different lengths, leap years throw off anything calculated by hand, and time zones add a whole extra layer when you're coordinating with someone on the other side of the world.

Counting days between two dates

The easiest reliable way: in Excel or Google Sheets, just subtract one date cell from another (=B1-A1) and it returns the day count automatically, accounting for leap years correctly without you having to think about it. Doing this by hand across multiple months is exactly the kind of thing that's easy to get wrong by a day or two.

Adding or subtracting days from a date

In Excel, =A1+30 adds 30 days to whatever date is in A1 - the spreadsheet handles month-end rollovers automatically, which is the main thing that trips people up doing it manually (does adding 10 days to January 25th roll into February correctly? Excel gets it right every time, hand math doesn't always).

Time zone conversion basics

Bangladesh Standard Time is UTC+6, with no daylight saving changes to complicate things on this end - but whoever you're coordinating with elsewhere (the US, Europe) likely does observe daylight saving for part of the year, which shifts the gap by an hour depending on the season. Always double check the current offset rather than assuming it's fixed year-round, especially around the daylight-saving transition dates in spring and fall.

A calculator for the adjacent question

If what you actually need is someone's exact age rather than a generic date difference, our Age Calculator handles that calculation directly, down to the exact day.