first wort hopping

[mike2brew]

Ive been playing alot with first wort hopping with great results. Is there an accurate formula for recipe calculations with this process?
Mike

[zbrew2k]

two resources: http://www.probrewer.com/resources/tools/bitterness.php

http://www.realbeer.com/hops/

I have targeted 35% utilization for calculating the total hop addition over the past 10 yrs and have pretty good luck. I split the load into two additions, and I count 0% utilization for my "C" hop addition (know thats not true). I boil for 90 minutes. 35% may be a bit high for "A" hops (first addition)...but again it works for me. Look at your process, and maybe start out with 30 in A position, 25-28 in B position, and less than that for subsequent additions.

There are lots of variables I did not address.