I recommend testing your kitchen thermometer when you first get it and then every 6 months on an ongoing basis. You should also do a quick test if you drop the thermometer or if it is exposed to extreme temperature fluctuations. For example, if you leave it outside in freezing weather and/or extreme heat, I'd do a quick test. I also recommend testing it whenever you question the results you are getting or if you are going to cook a very expensive cut of meat or are cooking for a special occasion. The test takes just a few minutes and it's so much better to take that time to test your thermometer rather than ruin your meal because of an inaccurate thermometer.