How can I know how long home-cooked food will stay good in fridge?

The USDA says to eat refrigerated leftovers within 4 days.

Be aware that how long you leave something out before refrigeration and the size of the container can shorten the edible lifetime. The gist is the longer it's warm, the more [likely] pathogens will be able to multiply to unsafe levels. A large container holds heat longer and takes longer to reach 40°F.

There's also some other interesting information on the linked page about safe storage durations for many store-bought items as well, including recommendations for how long it will stay good in the freezer. To be fair to @Allison's answer, many of the durations listed in that chart are 3-4 days or 3-5 days, though some are longer or shorter.

Food tends to become unpleasant before it becomes actually dangerous. I would try to eat things within 3 days of making them, though that's just my personal guideline and isn't based on any scientific data. If you aren't going to eat it that quickly, freezing it after it's been cooked and thawing it the day you want to eat it is probably a better idea.

The point of the fridge is to slow down the sex life of bacteria. So try and cool food down as quickly as possible - put slowcooker/casserole pots into a sink full of cold water for a 30mins before putting them in the fridge. A big pot of stew can stay warm in the fridge for hours if you take it straight from the stove.

Make sure things are well cooked before you store them, if it starts off with most of the bugs dead it will take longer for them to come back again.

Biggest problem in the fridge is cross contamination. Keep everything sealed. Put anything raw/defrosting on the bottom shelf and cover it if possible.

Apart from the obvious shelfish, mayonaise risky foods - one food to be careful of is rice. Regular boiled/steamed rice can grow nasty bugs very quickly even though it looks/tastes fine. Ideally use leftover rice the next day.

Finally don't worry - unless you are have some serious existing medical problem the worst you are going to get from last week's sausages is an extended time in the bathroom. Did your grandmother have FDA approved labels on everything she baked?

StillTasty has got lots of information about how long specific foods will keep for.

I've lived by a simple rule for many years now: if it looks ok and smells ok, it is ok. Just use your common sense.

I can tell you from experience that I have eaten leftovers that were many weeks old, with no ill effects. As Allison mentioned, if your food was cooked properly in the first place, it will become unpleasant long before it becomes dangerous.

1. I have found that food stored in GLASS containers lasts longer and tastes better, compared to plastic, though stick to USDA guidelines

2. Watch out for putting hot food in the fridge, it will warm everything else up. In the commercial kitchen I worked in, we would put the hot food (container) in an ice bath in the sink before putting it in the fridge

3. Get a fridge thermometer and make sure your fridge is very cold (1 °C)

4. Throw out bad food regularly, so it doesn't transfer smells to good food

5. Get some masking tape and a marker and write the date the food should be thrown out by (not the # of days, because you'll forget the starting date). Attach these near the fridge

I agree with Allison. I recommend that once you cook your food, prepare packages for each night of the week and freeze. (Identify each package and note date.) It takes a short time to defrost the pkg. and heat for your evening meal. In the event you don't get home for dinner you won't have to worry about spoilage and dollars going into the garbage.

I can share with you that I grew up with a Friday "Left Over Night Dinner" which we kids called "Garbage Night"! It was always great believe it or not. My mom would save whatever left-overs from M-Th. dinners. On Friday, she would heat up the left overs and, off course, with a family of 5 she always added a fish or a pasta and what ever was left was thrown out.

It is better to be safe than sorry.

A

I think Allison hit on the key point. Below 40 degrees F, dangerous bacteria are not multiplying anymore, but other breakdown processes are still happening. Some of these can even improve flavor the first couple days, some not so much. If it was safe when you put it in the fridge, and it doesn't smell rotten or have any obvious mold, there's minimal risk.

People have been doing without refrigeration for a long time. There's an evolutionary reason we naturally reject food that smells rotten.

In every professional kitchen I have ever worked in, no prepared food is kept for any longer than 7 days. Of course, depending on what it is you may want to throw it out before then, but I wouldn't eat anything that had been sitting in the fridge for any longer than that...

I have found it's important to cool hot food just to room temperature and then refrigerate right away. Putting it in the fridge still hot, or keeping it at room temp too long (more than an hour is the rule, but for me it's even less time) does not seem to affect the taste, but leads to unpleasant side effects like long bathroom visits. For example, when I make a stew I put it in shallow glass dishes and stir every 10 minutes so it cools evenly, then refrigerate enough for 3 days when it reaches room temp, and freeze the rest.