When they're slightly squishy, look yummy, and a gentle tug on them makes them come off the vine.

Those are my guidelines, at least ;)

When they turn red...you know...every gardener just knows...I like mine a little on the firm side so I watch and wait and when the time is right...I always know and you will too...

Pick lots of tomatoes and eat them all right away out in the garden before they get old and stale carrying them into the house. LOL.

Remember to always carry a salt shaker in the tomato patch. :-)

I never grew a bad tomato in my life and I hope you never do also.

Just before the tomato stalk joins the truss there is a little 'knee'. If a slight kink on the tomato breaks it off at the knee, it is ripe.

A ripe tomato should be slightly soft (unlike the grocery store ones). And as far as the color it depends on what type you planted red, white, yellow, green, bi-color....

The critters around here usually tell me when mine are ripe!
If I think one more day will make the tomato perfect...they always beat me to it.J