It I put 500:45:00 in a1
and &00:45:25 in A1
The in A3 =A1+A2, I get 1201:30:25

I do not understand "it stops counting after 1000 hours" please give more
details of your worksheet's layout
best wishes

--
Bernard V Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme
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"Nick" wrote in message
...
I am looking to calculate hours and minutes.
I want to calculate how long something has been running for by adding
hours
and minutes every week to the total.
The problem is it stops counting after about 1000hours. is there a formula
to count hours and minutes up to say 10000hours.