Simple. I don't. Well I haven't so far. Now, I have lived in and currently live in a state that has little or no requirements for homeschoolers. Homeschools in Texas are considered private schools. So it's really never been an issue for me.
I've heard friends talking about how they log their school hours. One kept a book in her living room and wrote down everyday what she did and how long it took. Just the thought of that overwhelmed me. I mean, that would just take me too long. I can't even have a conversation on the phone for more than 30 seconds without being interrupted.
You can google, "How to log hours for high school credit" and get some good answers. A basic rule is that if your child completes a high school level text book, they get one high school credit. Actually, many schools consider completing 75% of a textbook to equal one credit. I'll never forget the time a few years ago a homeschool friend of mine, who is a former teacher, told me that teachers rarely, if ever, finish a textbook. I had been homeschooling for a long time when I heard that. I had no idea. Boy, did I feel the burden of having to finish textbooks lifted! If you are curious about how many hours one credit would equal, it is generally considered to be 120-180 hours which equals 50 minutes/day, 5 days/week, 36 weeks a year.
So, my high school aged son needs a fine arts credit on his transcript (per his school administrator- me). He spends about 1-3 hours per week in our church choir. He may also go on a mission trip with them this summer. He will earn either 0.5 credit hours or 1.0 credit hours this year doing that. I'll wait until the end of the year, see if he goes on the mission trip, and then I'll figure that out. That might be the first class that I might have to sort of track hours to determine how much credit he gets.
I plan for my 2 oldest to go to a government camp this summer for a week where they will earn a 1/2 credit in high school government ("IGovern West" with Home School Legal Defense Association). They will have 60+ hours of study during the week! In addition, Luke, my 10th grader, will attend a 2 day chemistry lab intensive in March where he will complete (more than) all of the chemistry labs that a generally considered required for high school students. A chemist will teach the group and also give insight into college academics and professors.
What made me think of tracking hours was that today, for some unknown reason, I added up how many hours/per week we have Bible class. We have a 30 minute class five days a week so that's 2-1/2 hours per week. I never really added up how many hours we spent in any class before. It's the only class where we are all learning together. It's my favorite.
Sadly, Sophia will take a break from gymnastics until after the new year. Caroline is taking a break from horse riding lessons too. The club sports and kids' braces really add up!