Depends on the aircraft, as far as I remember:
Boeing 737: half of headwind component + gust, minimum +5, maximum +20. On autothrottle you always select Vref+5, the autothrottle logic corrects for gusts.
Embrear E-jets: same as above, except for autothrottle logic.
ATR 42/72: 1/3 of headwind OR gust (whichever is higher), minimum Vref, maximum Vref+15. I believe Airbus is something similar?
On the ATR -600 you just punch tower wind into FMS on final approach (e.g. 360/10/20) and the FMS does the rest.