Countersink/Spotdrill formula

Hi, Im not sure if I am doing it the right way.

For example, the hole is .125. I want to get .135 chamfer so I use 90 degree 1/4 spot drill.

.125/2 = .0625 depth and add .01 = .0725 depth to get .135 chamfer?

Is that correct?

Thanks in advance!