From Web TimeSheet has Ability to Sum Custom Columns that are Percentages.A new Custom Formula summary option is now available in reports. Unlike the Sum option which sums each value in a custom column after its formula is applied, this new option sums values for each column used in the formula before applying the custom formula. You can use this option to find the sum of percentages or other fractions.

For example, imagine you create a custom column to calculate % Billable with the formula (Billable Hrs / Total Hrs), and for one project 20 out of 40 hours are billable (50%), while for a second project 10 out of 50 hours are billable (20%). If you select Sum for this custom column, Web TimeSheet will sum the calculated percentage for each project, giving a value of 70%. However, if you select Custom Formula, Web TimeSheet will sum the billable hours (30) and the totals hours (90) before applying the custom formula, arriving at 33.3%.