Question on MFP set up

[Poppysball]

I’ve just set myself up on mfp but I’m unsure how it works out how many calories I can have a day.

Where it asks if you are sedentary, active etc I put in lightly active and then put in my goal of doing 3 x 30 min exercise sessions per week. It has set my daily calories to 1400.

My question is do i still need to input my daily exercise into the diary and what happens if I don’t manage to do 3 per week? Will this mess it all up?

The number of calories yu 'get' for exercise is rather a loose estimate (better than it used to be, but still not to be relied on)

I decided not to 'eat' my exercise calories when definitely needing to shed weight. I did track though - but did it by setting it on low activity, and then adding what I'd actually done.

I guess that if you set to one of the more active levels, it's better not to input what you've already counted in deciding that level.