Sum values in Column A, based on dates in Column B & if value in Column C = True

Thanks for reply Jonmo,

I tried that formula already and it didn't work for me. If doesn't give an error, just return a zero value.

Either the values in B (and or your start end dates) are not really dates, they're just text strings that look like dates
Or the values in A are not real numbers, they're 'Numbers Stored As Text"

What do these return

=ISNUMBER(E1)
=ISNUMBER(F1)
=ISNUMBER(A1) <- filled down to the end
=ISNUMBER(B1) <- filled down to the end


It would also be helpful if you could attach a sample book.