Hi there

I am trying to calculate our On Time Delivery. I want this as a simple percentage of jobs. I have got this running in the following way:

Column M - Estimated Delivery dates
Column N - Actual Delivery dates
Column O - =IF(SUM(M2-N2)>0,1,0)

Then I have calculated On Time Delivery as: =SUM((SUM(O2:O252))/(COUNTA(N2:N252)))

This seems to work fine. My problem is, if we enter a date in Estimated without a corresponding Actual date, the formula for Column O fills out anyway and improves our On Time Delivery Percentage. How can I set this up so that the formula doesn't calculate if there is no data in Column N?

Any help much appreciated

Thanks,

James