How does a criterium in bike racing work? When it says that the race is 30 minutes + 5 laps, what's it mean?

I've been cycling for over a year now and I'm thinking of trying out a local crit. I'm just wondering what exactly the format is. Every race lists a time plus laps. I'm kind of confused and would appreciate the help.

How is the winner determined then? By who finishes the most laps or who finishes the last 5 laps the fastest?

The winner is the first person across the finish line. Crits are run in different formats. Where I live, they are usually listed by distance or number of laps. Thus, a 15 mile crit could be 15 laps on a 1 mile circuit or 20 laps on a 3/4 mile circuit. How long a 15 mile crit takes will depend on the ability level of the group, but a good estimate is anywhere from 22-28 mph for the group. Womens and juniors races are typically slower.

Some crits are run by time, thus they will let you race for 20 min and then ring the bell and call "5 laps to go." This doesn't mean that no one races for the first 20 minutes, it just lets people know that the final sprint is coming up.

The idea behind the criterium is to maintain high speed, to draft and use the group to your advantage. There are really two ways to win (or do well in a criterium). The first way is to stay in the group for most of the race to conserve energy and then wait for the final sprint to try and win the sprint. This is a good strategy for someone that is a good sprinter. The other way is either early, midway or late in the race, one or more riders will try to break away from the pack and get out front. Once they get a time gap over the main field, depending how strong they are, and how hard the main field chases, they will either stay away to the finish, or get caught before the finish. And that is the excitement of any bike racing.

The riders that can successfully break away tend to be good time trialists, ie they can ride solo at high speed without needing to draft off other riders. Sometimes one rider can do this in a solo break and survive, but most can't. A hard chasing pack can easily do 30 mph and most racers can't sustain that speed on their own for more than a minute.

You complete laps on the circuit for 30 minutes (beginners may do only 20 laps, pros may do 30 laps). At the end of 30 minutes no matter the lap count you do 5 additional laps. This helps promoters control the scheduling of the races (as they know how much time each race will take). Hope this helps.

Each racer will do the course for 30 minutes, and when the time is up, they will complete 5 more laps, and the person across the finish line first is the winner (assuming that everyone stayed together, and thus had the same lap count).