If your looking for a free, pretty simple one.  Check out http://handicap.golfdigest.com/    

If you belong to a club, they should have a computer that you enter your scores into to establish your handicap.  If not, you can join a golf club online.  Google is your friend here.  I found several online handicap services.  One that looked intriguing was www.myonlinegolfclub.com.  Don't know anything about them, just using this as an example.

Good luck.

If you do not have access to the GHIN handicap system (www.ghin.com) you can get a pretty good idea on your own. If you take the best 10 scores of your last 20 scores and average them. Then take 92% of that number and this will be pretty close to the number you would get from GHIN.

Hi Will,

Here is the formula that is often used.

[(Your score - course slope) x 113] / course slope

this will give you the index for the round.

after 5-6 rounds take the lowest

after 7-8 rounds average the the 2 lowest

after 9-10, average 3 lowest

after 11-12, average 4 lowest

after 13-14, average 5 lowest

after 15-16, average 6 lowest

after 17 rounds, average 7 lowest

after 18 rounds, average 8 lowest

after 19 rounds, average 9 lowest

after 20 rounds, average 10 lowest

Now take that average and multiply it by 0.96 and that will be your handicap.

I like to use the formula to give me a target score to beat at a new course or tee position. I'll take my oldest best index score and multiply it by the slope. Then multiply that number by 113. And finally add the the rating to see what score I need to beat in order to improve my handicap rating. This number helps me to manage my round so I know when a risk crosses the boarder to unnecessary.

My bad!

This should be [(Your score - course rating) x 113] / course slope