Column E - User inputs date of test
Column H - Indicates number of days since last test (=DATEDIF(E16,I16,"yd")
Column I - Hidden Column with the current days date to give number of days since last test in column H.
What's happening in Column H is that from the value 365, the value in volumn H reverts back to 0 and restarts the count and i need it to continue.
Solved by G. Q. in 17 mins