I never really thought about a formula. I've only used a guide twice. Once the guy was self employed (not working through an outfitter). The only person he had to share the money with was his wife (and daughter) which tells me he probably got to keep very little of it for himself...

I tipped him 20%. My son and I had a great time, caught some fish, and learned a lot about the streams in that area.

The second time was in Yellowstone. My son and I had a great time with our guide, he treated my son with respect (not like a little kid) and we caught some nice fish. He was very friendly, fed us well, had a good sense of humor, all in all it was an excellent day. I tipped him about 25% or a little more and handed him a very fine (Fuente Opus X) cigar at the end of the day.

I never really thought about a formula other than if we had a good time and the guide treated us well, he's going to get a decent tip. If he's a jerk, lazy, vulgar, etc. then he wouldn't get much if any of a tip.

The guide can't make fish bite. As long as he's putting the client on the fish and putting you where you can catch fish, he's doing his job. Some days you catch a lot of fish, some days you get skunked.

Jeff