@Indy51 's link to the phil aunt website is brilliant. There's even an explanation as to how the calculator is built.
And
@Gabby22 's comment about choosing healthy carbs is correct, but unfortunately we are all different with what constitutes 'healthy'.
Some can eat bread and wheat - but it spikes my BG terribly. Same with rice, potato and sweet potato.
The best solution is to get a blood glucose monitor (if you haven't already got one), and test to see what foods are best for you. For me, healthy carbs are mainly veg and berries.
And please don't be dismayed by the amount of fat the calculator suggests. You can always work up to it, and stop when you feel satiated. Just avoid processed fats, heat treated ones and margerine. Go for olive oil, butter, coconut oil, hempseed oil, and fish oils, where possible.
My body feels better and better the lower carb I go, but we are all different, and your optimum carb level may be anywhere from 10g to 200g a day. But it won't take you long to discover it.