There are four factors that come into play here.
The type of bike: The most popular bikes come in two flavors – road bikes and mountain bikes. Other types such as commuter bikes and racing bikes fall between the spectrum of these two. The frequency of bikes’ pumping frequency will vary quite a bit between the two. Most city bikes have required more frequent pumping than mountain bikes. The reasons are twofold. First, the city bikes have thinner tires whereas the mountain bikes have thicker ones. Hence, for the same person of the same weight will need to pump their road bike more often.
The rider’s weight: Everyone has a different body weight and height. As a result, people buy bikes with frame sizes based on that factor. So, when all else is equal, a heavier person would need to pump more than others. In my case, I am 5’9’’ and 145 lbs – so pretty average. I pump every once a month even before the tires get flabby. But if it was my sister who I imagine is half my weight were to ride the same bike, she would be fine. Pumping it once in two months.
Tire width: Generally, mountain-bike tires’ width can range between 30mm and 44mm. Whereas, road-bike tires’ width is usually lower e.g., between 19mm and 30mm. The bigger the width the stronger its rubber. Road bikes will deflate faster than city bikes. Other factors like usage come to play here as well. Based on that, after a while, you will be able to tell how often you are losing pressure and come up with your own schedule.
Observation: Before you ride, use your hands to check if the tire is limp. If so, pump it. If you have leaks or a puncture, you will lose pressure very fast. So, using a gauge is always a good idea.
Finally, my pro-tip would be to get yourself a compact tire inflator with a gauge in it. This way it will have your back when you ride and if things go wrong, it will be able to show you what kind of pressure you have. Besides that, if it is low, you can inflate it on the spot.