Net carbs is where you subtract fiber from the total amount. Fiber is a carb that your body cannot digest so it does not raise your blood sugar levels or trigger an insulin response.

So let's say you look at coconut flour.. It's, like, 20 carbs per cup but it's 15 fiber (this is an estimation but it's actual pretty close).. You subtract the fiber so it's only 5 carbs for that cup. It's so handy when you need to bread something.

That's how I've come to understand net carbs

MFP does not give you net carbs - under your diary settings, you can change which nutrients are tracked. I set mine to Carbs, Fiber, Protein, Fat, and Sugar. I'll easily hit 50-60 g carbs a day, but 20-25 g fiber, so still well within ketosis ranges.

You just have to keep an eye on Carbs - Fiber throughout the day and do a bit of mental math.

The one really annoying thing is if you try to set a macronutrient ratio of Carbs/Protein/Fat at, for example, 10% / 20% / 70%. Fiber is basically non-caloric because we don't digest almost any types of it, but MFP will calculate that 10% with the fiber included. Which means, your actual percentage of (net) carbs for the day would be lower, and you could have had some more veggies/fruits/nuts/whatever if you wanted. Oh well, just something to keep in mind.