1) The size of the female. Larger females tend to have more babies than smaller females.
2) The age of the female. Older females tend to have more babies than younger females.
3) The water temperature. Warmer water temperatures can lead to larger broods.
4) The diet of the female. A healthy diet can help the female produce more eggs.
In general, a guppy can have anywhere from 10 to 100 babies at a time. The average brood size is around 30 babies.