The cutlet alone is 442 calories, and 30g of that is fat, which means 270 of the 442 calories are fat calories. A 120g piece of raw pork loin has about 15g of fat to begin with. The panko crust then soaks up another 10 to 15g of oil in the fryer. That is why a hire (fillet) katsu, made from a leaner cut, comes in about 100 calories lower at the same weight. The crust is identical, the meat underneath is not.
The teishoku is where people lose track. Matsunoya's rosu katsu teishoku is 830 calories: 442 for the cutlet, about 250 for the rice, 28 for the miso soup, and the rest is cabbage, pickles and sauce. Many tonkatsu specialists offer free rice and cabbage refills, and a second scoop of rice is another 250. A 'refill twice' lunch is 1,300 calories, more than a full day of eating for some people, for about 1,000 yen.
Tonkatsu sauce is 25 calories per tablespoon, not terrible. The cabbage is 20 calories for the whole pile and worth eating first. The other thing to know is the size range. A regular cutlet is 120g raw. The 'thick cut' or 'rib loin' cutlets that specialist shops push are 180 to 200g and 650 to 700 calories on their own, so the same teishoku becomes 1,100.