Macros

The MFP default macros aren't terrible for most people, as long as one is not trying to lose weight too fast for current size, IMO.

Another approach is described here:

https://community.myfitnesspal.com/en/discussion/819055/setting-your-calorie-and-macro-targets/p1

Counting calories while trying to hit macros is pretty much the same thing as counting macros: Each macro has a characteristic calorie level (carbs & protein 4 calories per gram, fats 9 calories per gram, alcohol 7 calories per gram). So, other than rounding errors and such, it comes out about the same.

However, if you need a calculator that's specifically labeled IIFYM, that I can't help with - sorry. Maybe someone else can.

BTW, there's a really good option (IMO) for protein specifically:

https://examine.com/nutrition/protein-intake-calculator/

This is from an evidence-based site that's generally regarded as neutral (they don't sell supplements; they sell more in-depth research reports). The beauty of this calculator, IMO, is that it's very transparent about the underlying research justifications for the recommendations. There's a whole, good document about protein requirements that talks about it, with links to the research:

https://examine.com/guides/protein-intake/

The calculator also has the advantage of not requiring you to provide your email address in order to get the result.

Yeah, there's still fats and carbs to worry about, beyond protein. But protein is a biggie, and carbs are pretty individual (IMO). Only protein and fats are "essential macronutrients" in the technical sense that your body can't manufacture those itself from other nutrient intake. It can manufacture carbs, in effect.