What you could do is to create a variable to hold the datetime when the timer is first started, e.g. variable = Now, and everytime you need the time, subtract the variable from Now, to get a timespan representing the time so far. To convert the timespan into a string, use Now.Subtract(variable).ToString() and split the string by the "." to remove the fraction of seconds.
Do you just want to add the total elapsed time to some time?
'Put at the top of your form Public StartTime As DateTime
Public EndTime As DateTime
Public NewTime As DateTime
'Move start and end time line to where they start and end. StartTime = DateTime.Now
EndTime = DateTime.Now
'This will add the elapsed time to any DateTime value 'NewTime' Dim ts As TimeSpan = EndTime.Subtract(StartTime)
NewTime = NewTime.Add(ts)
'Takes care of adding hours,minutes and seconds. TextBox1.text = NewTime.ToShortTimeString
If that is not what you mean by 'I need to do some calculation'
Timespan values can also be accessed as integers to use in calculations also: Dim eSeconds As Integer = ts.Seconds
Dim eMinutes As Integer = ts.Minutes
Dim eHours As Integer = ts.Hours
NewTime = StartTime.AddMinutes(eMinutes)
Hope that helps, If you still need answers post the code you have (just the bits dealing with the calculations and timer, not the whole form) and be really specific as to what you want to do.