Hi Capt Smiley,
As ever, it depends on what aeroplane you are flying and for what purpose. For a private flight you can do what you like, there are no regulations beyond the captain's obligation to ensure that the flight may be safely conducted etc etc. The CAA have a very good leaflet on Aeroplane Performance here
http://www.caa.co.uk/application.asp...e=sercat&id=21 it's well worth a read.
You should also read the Pilot's manual for your aeroplane. In the performance section it will have data but this may be measured data, gross data or nett data with safety factors already included - read carefully so that you know what you are starting with. Often but by no means always the 150%/50% wind factors are included; you can tell if the data is in graphical form because the lines on the wind correction part of the graph will show a marked kink as they cross zero. this means you can use raw wind data and the different gradient of the line will correct for 150% of the tailwind and only 50% of the headwind.
AIC 67/2002 (pink36) covers performance in light aircraft and it recommends (Section 5.4.1) that not more than 50% of the headwind and not less than 1505 of the tailwind should be used; it's also well worth a read.
If you flight is public transport there will be a performance manual and you must do exactly what it says as this and only this will have been approved by the CAA.
Happy landings!
3 Point