Yeah, never used to calculate drift in the air or on the ground during IR. Just follow the needles and experiment with 5deg drift at a time. All you have to do is know which way the wind is blowing from. It works on the ILS, too. You can even get away without calculating drift in the Hold. Again you just need some idea of where the wind is coming from. In the hold, just fly a heading into wind, then aim to be on the gate at 2.8d from the beacon and you can't go wrong. It's exactly the position to be in regardless of wind. Worked everytime for me.
If you want to work out drift then this is what to do.
At 150K (Seneca cruise) max drift is 4deg for every 10 knots of wind ie 15kts = 6deg. etc.
Then use clock code to work out fraction of drift applicable. ie when wind is:
60 deg off heading = all the drift applies
45 = 3/4 of the drift
40 = 2/3
30 = 1/2
etc
eg: HDG = 340deg
wv = 320/25
max drift = 2.5 x 4 = 10 deg
clock code = 20deg therefore use 1/3 of 10deg
ans: drift = 3deg
In the hold at 120Kts use 5 deg per 10kts
At 90 kts (warrior, or ILS) use 6deg per 10Kts.
Hope this helps. Just practise doing the numbers over and over whilst driving or doing some other task. becomes easy after a while - you can even do it on the approach.
Good Luck