When your tomatoes turn red they are ripe.A lot of time bugs and birds feast on your tomatoes just before they are ripe leaving you with a tomato rotting on the vine.
It is best to leave your tomatoes on the vine as long as possible. Vine ripened tomatoes have the best flavor, with lots of extra vitamins and nutrients.
If you are losing the battle with the hungry bugs and birds in your garden and your tomatoes are getting damaged and rotting on the vine then pick them. Put your tomatoes in a paper bag or set them out on the counter to finish ripening on your back porch or in your kitchen window.