Three days in the fridge, then reheat gently.

Three to four days max, and the best way to reheat is low and slow with a little moisture — skip the microwave unless you want a dry, fishy hockey puck.

Cooked tuna (like from a can you sautéed or a fresh steak you grilled) stays good in the fridge for about three days, maybe four if it was really fresh and sealed tight. After that, the texture and flavor go downhill fast. Trust your nose more than the calendar.

For reheating, the microwave is the enemy. It will zap the moisture right out. Instead, toss the tuna back in a skillet with a splash of water, broth, or oil. Cover it and heat on medium-low for a couple minutes, flipping once. That steam will keep it tender. Or you can wrap it in foil with a teaspoon of butter or stock and pop it in a 300°F oven for 5–7 minutes.

If you’re eating it straight out of the fridge on a salad or sandwich, that’s fine too. Cold tuna isn’t bad — just don’t try to pretend it’s fresh.