Transitioning from slimming world

I know you don't really mean it about eating all and only Freddos (whatever the heck that is ), but yes, eating that number of calories would make you maintain weight, with a couple of caveats.

First, the 2400 is just an estimate based on statistics from research studies. It's the average for people with your details (size, age, etc.). If you're exactly average, it'll be spot on. For most people, it'd be close. For a few people, it could be a little off, either high or low. For a very, very few rare people, it could be significantly off. That's all kind of the nature of statistical estimates.

What you do is set up the calorie estimate, being as accurate as you can about your activity level and such (no need to agonize over it, but be honest and read/respond carefully). Then, you follow it for 4-6 weeks (at least one full menstrual period if you're a pre-menopausal woman, because menstrual cycles often include water weight fluctuations, and you want to compare the same point in two or more different cycles). After you do that, you will see whether you've gained, lost, or stayed the same weight. (It's highly unlikely you'll gain much if any, so please don't panic about that possibility.)

Then, adjust your intake based on that test period. Pretty straightforward.

One thing to know: There are two basic approaches to getting a calorie goal.

If you let MFP estimate your calories, it wants you to set your activity level based on work and everyday home life, not including intentional exercise calories. Then, you log exercise separately, and eat those calories, too. That means you get to eat more when you're more active.

The other approach is to use a TDEE calculator, of which there are many. They ask you to estimate your activity level including intentional exercise, and give you a calorie goal that includes that, too, so you don't then log exercise and eat it back separately. That will give you the same calorie goal every day whether you work out or not . . . but the catch is that if you skip planned workouts, you may gain weight.

You can also synch some brands of fitness tracker to MFP, but that's a more detailed discussion.

The other thing is that - as you know, in reality - nutrition really is important, for health and energy level. If you really did eat only Freddos, you would be poorly nourished in the long run. I know you don't really intend to eat like that, but the point applies to other forms of poor overall nutrition, too. With poor nutrition, eventually your health and energy level are likely to suffer. That may result in fatigue, inactivity, and weight gain at your "maintenance" calorie level, simply because you're less active.

So, you really want to pursue adequate overall nutrition, for long-run weight maintenance. The good thing is that as long as you don't have any doctor-diagnosed nutritional deficiences now, you can take some time dialing in better nutrition (because malnutrition is a long-term thing, not instant), and logging on MFP can help you to do that.

Best wishes!