All of my new tomatoes have rotten spots on the bottom.
Rotten Spots on New Tomatoes
Certified GKH Gardening Expert
That is blossom end rot. It is actually a nutrient deficiency that is normally brought on from rapid growth on the plant or too much water. This article will tell you more about it and how to deal with it: https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossom-rot.htm