Plug in your age, gender, current weight, height, formula (normal/lean mass), activity level, and weight goal (lose/maintain/gain). Click calculate and it will tell you how many grams of carbs, protein and fat you need to be in ketosis.

I suspect it's an average estimate, and will only give you a ball-park answer, but it's a good start.

https://healthyeater.com/keto-diet-macros

I have no affiliation with this page. I've been keto for decades, but a relative wanted info and I found this for her, and thought I'd share it with the group.

Thanks for the link, Bob. Pretty cool tool. Plugged in my data and it’s close on amount of carbs, very close, but slightly low on protein, and high on fat. The recommended amount of fat doesn’t surprise me, as this is based on a traditional keto “diet.” I’m close on this with more protein which I cover with low-fat Greek yogurt supplemented with a good quality whey powder. The total calories I consume are also a bit lower, as I don’t need to make any effort to limit calories due to how I eat. Good stuff.

I found a few other calculators, but they wanted to know exactly how much exercise per day, BMI ration and so on. I suppose they might give a more exact estimate, but I figure this is close enough.

I've always gone by under 20 net carbs and twice as much fat as protein. This calculator gave about the same for losing weight, and allows more carbs for maintaining.

I don't plan on changing. I'll blow ketosis on Christmas dinner. My kid sister is making my mother's recipe for cavatelli. Italian comfort food.

Blowing ketosis once or twice a year isn't really a bad thing. I'll gain a pound, a few days later when I'm back in Ketosis, it'll go away.

My relative was taking advice from a gym trainer, who said under 50 carbs a day meant you are in ketosis.

Me? I wouldn't take any scientific advice from a gym trainer.

Any tool that uses BMI in its algorithm has already lost the plot. Most of these tools use BMI, so they’re more fun with general results.

Hah, I would never use a fitness trainer. Recent resistance training research has changed dramatically with many nuances. I prefer to develop my training program with input and methods from Doug McGuff or Brad Schoenfeld. You don’t need to abuse yourself with long, multi-day workouts during the week, but you won’t defeat sarcopenia by simply going for walks. But I’m getting off topic.

I would never use a trainer either, and never have.

It would remind me too much of the jerk we had in PE (Physical Education) class in High School, who thought he was our Drill Sargant.

Don't tell me what you think I should do, I can figure that out myself...☺