I have a query that calculates the hours worked from dates which includes times.

Question

Editorial Team

Asked: May 23, 20262026-05-23T13:16:53+00:00 2026-05-23T13:16:53+00:00

e.g 1/07/2011 7:00:00 AM – 1/07/2011 5:40:00 PM – 0.5 = 10.166666

The SQL is

    SELECT    entityID, StaffID, ActualDate, 
    DATEDIFF(minute, StartTime, EndTime) / 60.0 lunch AS HoursWorked
    FROM      dbo.qasiteTimesheet

StartTime and EndTime are both datetime type.
Lunch is numeric(9,1).

If I add whole hours e.g 6:00 AM – 5:00 PM it works fine, but add 34, 10, 2 it rounds up incorrectly.

What am I doing wrong?

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Editorial Team · Answer 1 · 2026-05-23T13:16:53+00:00

Editorial Team

60.0 is decimal(3,2) and the rules for decimal division are quite complex.

lunch decimal(9,1) too, so you can never have more than 6 minute accuracy here

Put together, it’s a simply precision problem.

I’m not going to work it out fully (you can see my answer here) so try this, or an explicit CAST, or some combination

(DATEDIFF(minute, StartTime, EndTime) - (60.0*lunch)) / 60.0 - AS HoursWorked

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