You can try typing the above (in the subject line) into the search box at upper left of most pages, there's been a lot written here about it. In the meantime here's a nice little piece about it:
"Why does it take so long for tomatoes to ripen? There are several factors that affect ripening, including amount of sunlight, optimum temperatures, excess plant growth, lack of water, too much water, or too much fertilizer. It takes a standard-size tomato 40 to 50 days after blossom set to reach maximum size. The larger the fruit, the slower it will ripen. Therefore, late planting can cause tomatoes to ripen later than expected.
If the plant has heavy fruit, it will take a lot of energy from the plant and can delay the whole crop turning red. Tomatoes need sunlight to ripen. Plants with excess plant growth can reduce exposure of fruit to the sunlight and delay ripening. If this is the case, remove some of the vines to expose fruits.
Temperature is crucial to tomato fruit ripening. Red tomato pigments, lycopene and carotene, are produced between 50 to 85 degrees Fahrenheit. These pigments are necessary for the ripening process.
The optimum temperature range for ripening tomatoes is 68 to 77 degrees Fahrenheit. Extreme heat or cool temperatures will delay ripening. The longer temperatures stray from the optimum, the more stress to the fruit." https://www.illinoistimes.com/gyrobase/Content?oid=oid%3A8194
So temps much above 85 slow down ripening and above 100 they won't ripen at all. Too much nitrogen encourages the plant to focus on plant growth not fruit production/ ripening... To encourage ripening stop fertilizing, if the plant is very leafy and the tomatoes aren't full sized, maybe cut away a few leaves so the fruits get a little more sun (but don't overdo, they can sunscald). If the tomatoes are full sized (they don't ripen until then) and you are desperate, you can put a paper bag over the fruit and band it around the stem. This holds in the ethylene gas, helps it ripen.
You didn't say much about what conditions (weather etc) your tomatoes have had, how the plants are doing (are they huge, full size, stunted, have any other problems), how you've been treating them, re fertilizer, etc. If the above doesn't answer your question, write back with more info.