talking about accumulation factors in introduction to financial math, for compund interest accumulation factor, we have

(1+ i) ^t = (1+i_m)^(T_m)

where i_m means interest expressed in months

and T_m time in month

Then it says T_m= t x m

why? I mean 1 month= 1 year/12 that is T_m= t / m

I am getting confused. Thanks for all your help.