I'm adding times that I worked on different projects. When I add the times per day the result is OK. When I add the hours worked per day the first week total gives the correct result, but the other weeks give a result of zero hours. I do not see a difference in how I have added the daily totals first week: =SOM(AK3:AK9) = 25:41; second week =SOM(AK11:AK17); =0:0; see image. The format of the cells is equal (I did a copy paste for the week and the week totals) Any suggestions what causes this problem?