Honest answer: 420 kcal is a fair estimate for a standard bowl, but this is genuinely hard to pin down precisely because every stall makes it differently. Bone size varies, some joints are meatier, and the amount of marrow you actually extract changes everything. Treat these numbers as a reasonable ballpark, not lab-tested figures. The biggest driver of calories here is not the meat or the broth, it is the marrow. That 35g of marrow packs 120 kcal on its own, pure fat, and it is so easy to eat because it basically melts. The beef shank meat itself is actually great for dieting: lean, high protein, and very filling. Bro, 180g of cooked beef shank with 33g total protein in a bowl is not bad at all.
What actually changes the maths is whether you eat the marrow or not. Skip it and you are looking at 290 kcal, eat it all and you are at 420. Some stalls give you a massive joint or even two bones, and then you are easily at 750 kcal or more before you even add rice. The broth is almost a free pass at around 25 kcal for 300ml, so drink as much as you want. If you want to eat this regularly while losing weight, the move is simple: order one bone, eat all the meat and cartilage, leave the marrow or only eat half. You still get a hot, filling, protein-heavy meal for under 300 kcal. That is a win lah.