Time Addition problem in Excel worksheet

[John Rabbit]

I have an unusual situation where I am subtracting one cell from the previous to give me the duration; I am then trying to add up the result cells which works well when adding 3 cells; however when I add a fourth or more cell the result goes skewed .

Example where it works by using Auto Sum
10:17 AM 4/01/12 4:43 PM 4/01/12 6:26
9:23 AM 5/01/12 4:43 PM 5/01/12 7:20
10:17 AM 6/01/12 4:43 PM 6/01/12 6:26
Total 20:12

Example where it doesn’t add up (still using Auto Sum) just by adding one or more extra rows – why?
10:17 AM 4/01/12 4:43 PM 4/01/12 6:26
9:23 AM 5/01/12 4:43 PM 5/01/12 7:20
10:17 AM 6/01/12 4:43 PM 6/01/12 6:26
10:17 AM 7/01/12 4:43 PM 7/01/12 6:26
10:17 AM 8/01/12 4:43 PM 8/01/12 6:26
Total 9:04

[martindwilson]

format cell as [hh]:mm

[DonkeyOte]

Disregard below... I suspect mdw has resolved your issue !!

Auto Sum won't necessarily reference new rows if inserted above / below the first / last row being aggregated.