Is the bottom discoloured, like a dark spot? Could be blossom end rot - I usually throw those ones out.

Depends on what is causing them to go soft on the bottom. It could be many thing from just left on the vine too long to a disease. Post a picture of a couple of them.

If you pick your tomatoes at color break and let them finish ripening inside instead then you don't have to worry about disease or pest or weather damage causes. If you do any reading over on the Growing Tomato forum here you'll find that most experienced tomato growers do that.

Dave

I have been letting mine ripen indoors and they taste fantastic, nothing like store-bought. I agree with Dan. Let them ripen indoors once they start color breaking.

Here's a pic of them

Well the tops of them have what is called yellow shoulders and uneven ripening. Those conditions are caused by poor growing conditions - primarily overly wet soil, temperature extremes, low potassium, inconsistent soil moisture levels and periods of excessive heat or cold. You can learn much more about it over on the Growing Tomatoes forum here..

The one bottom showing that looks like it might have some soft spots is also caused by uneven ripening. The soft spots have ripened much faster than the rest of the fruit. Just cut the soft spots out and eat the rest.

Again you can eliminate some of this by picking the fruit at color break so that it isn't exposed to the temperature extremes and by stabilizing your soil moisture levels better.

Dave

Here is a link that might be useful: Causes of uneven ripening and yellow shoulders