Calculate base on dynamic columns

[minhhieule89]

I have a table similar like below, I want to do a formula so that depends on the value of the first row (T1, T2 or T3) it will take the corresponding value and subtract the Date column then sum the total value.

ID	Date	T1	T2	T3
1	1/1/2017	7/1/2017	8/1/2017	9/1/2017
2	1/1/2016	7/10/2017	8/15/2017	9/10/2017

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[mart37]

do you mean this: =SUMPRODUCT(C2:E2-B2)