If every day…?

I've never completed a diary entry.

TL/DR: It's overly simplistic. Calories in can be managed with relative consistency and accuracy but in my experience calories out can be highly variable day to day and week to week with variable activity and that variability makes the equation pretty ridiculous. YMMV.

IMO it's pretty gimmicky and overly simplistic. Even if you're consistent, not every day is going to be exactly the same. Even if you keep the calories in relatively consistent (and accurate), your calories out are going to vary.

For example, I have an office job for which I'd say on average I would put myself as sedentary. But I have days where I'm up and down quite a bit visiting this office or that office or I have meetings at the building across the street on the third floor and I'm just generally moving around more and not at my desk all that much. Then I have days where I'm up and down some to go to the printer or the restroom or go to the breakroom or go talk to a colleague down the hall, etc...which is kind of a normal day. Then I have days when I'm completely immersed in my work and I basically don't leave my chair other than a bathroom break.

Then there's home life. Some nights not much is going on and I get home and maybe help with some homework and eat dinner and watch some TV and go to bed. Other nights I'm shuffling kids to and from soccer practice or cooking up a mess or out in the yard doing some work and don't sit down until basically bed time. Weekends are pretty variable too. Some are lazy and relaxing while others are busy and we're running around like chickens with our heads cut off trying to get kids to and from soccer games and running numerous errands or doing a lot of house work or yard work.

And that's just day to day stuff. I'm not training for anything at the moment so most of my exercise is active recreation which can be pretty variable as it's not particularly structured. I'm dropping one of my kids off at soccer practice this evening and that will give me time to get out for a quick 30-40 minute ride before I have to pick him up and get home to make dinner as it is one of my nights to cook...Saturday morning I'm meeting up with some buddies to go mountain biking and we'll likely be on the mountain for at least 4 hours but probably more like 6+. That's a massive swing right there.

As you're seeing, people around here mostly eye-roll at the 5-week projection. On top of what everyone is saying about the ridiculousness of every day being consistent, MFP is at base only giving you a calorie goal that amounts to the average for people demographically similar to the values in your MFP profile.

You're a unique individual. Your MFP goal may be spot on for you, or close . . . because most people are close to average. Or, you could be statistically unusual for some non-obvious reason; or you may've guessed wrong at your activity level setting or exercise calorie estimates. (Even if you get activity calorie estimates from a synched fitness tracker, those are just more sophisticated calorie estimates based on average people, not actual measurements of personal calorie burn.)

A better way to look at this is that after 4-6 weeks minimum - whole menstrual cycles if that applies to you - you'll have some idea whether your MFP goal is spot-on (or close) for you. If it is, you're good to go, as long as you're not trying to lose unsustainably fast. If actual results are further off than you'd prefer, you can adjust your intake to dial in a sensible loss rate.

The 5 week prediction is more like the Magic 8 Ball: Kind of a party trick.

It is wildly optimistic, but amusing.

I've never had 35 days in a row that were exactly the same.
In general, looked at over time, MFP underestimates how much I will lose, or how much I can eat to maintain.

Ive been logging for 210 days in my diary. Lost 60 lbs since 4/1/22. I needed to cut sodium due to crazy high blood pressure (also was 290 lbs ugh)
My calorie allotment is 1580 daily and im eating super clean. I use my fitbit to earn back calories as well so there are special food days & I eat out once per week usually but i log absolutely everything & weigh my food too. Im looking at sodium content only to try and stay under 500-1000mg sodium. The calories fall into place when you do this automatically. I rarely go over 1100-1300 calories per day & I eat all day pretty much. Having said all that, i do find it to be pretty accurate. Maybe a bit over estimated but darn close. Its nice to see the numbers that ive not seen in a good 10 years. Ive got 80 lbs to go...All the best!!

Last time I did MFP, years ago, I quit because I NEVER was able to match the 5 week predictions, and it made me feel like a failure. I was able to stick to the diet, but my weight loss always slowed and plateaued before I met the predictions.
I think the feature should be removed. This time around I am ignoring it. I am having success, lost 10 lbs in 7 weeks, even though the stupid predictor says I should have lost 13-14. So far, havent hit the plateau yet, but with 20 lbs left to lose, i figure I will have some slow downs in my journey.