Why is 5 week weight estimate wrong?

glh72
glh72 Posts: 2 Member
Hi, I'm curious why the 5 week weight estimate (when you complete diary at the end of the day) sometimes seems wrong.

I've set a goal of losing 1kg a week, so assumed if I take in less calories in a day than my allowance, my estimated weight in 5 weeks would be a loss of at least 5kg - but it's not always so.

Yesterday for example I was 100 calories under, but my weight loss was only projected to be 3.5kg.

It's annoying to think you're doing well then the app tells you you're not!

Any idea why this is please?

Replies

  • jillybeansalad
    jillybeansalad Posts: 239 Member
    edited March 2021
    There's a lot more involved in a weight than fat. There can be variances from water retention, inflammation, etc. Also, if you under eat (1kg/wk is pretty aggressive already) you may lose muscle which will cause your metabolism to lower as well. You still need to support your lean mass with the applicable macros too.
  • Lietchi
    Lietchi Posts: 3,799 Member
    edited March 2021
    It's totally unreliable, for so many reasons.
    But one factor that can explain a lower projected weight loss than expected when under your calorie goal is when you've chosen a weight loss rate that is too aggressive for your situation. 1200 is the lowest calorie goal for women and 1500 for men, no matter what weight loss rate you select. So your calorie goal might not be low enough to allow for 1kg weight loss per week. Basically, you're not heavy enough to lose weight safely at that rate.
  • autumnblade75
    autumnblade75 Posts: 1,654 Member
    If your calorie needs don't total 2500 before the deficit is applied, the app will not apply the full 1000 calorie deficit to your goal, because that would require a goal of less than 1500 calories per day, which is the bare minimum that might possibly be healthy for short, old, sedentary men. That will add up to less than your selected rate of weight loss in the 5 week estimate.

    You could be more active, and select a higher activity level. Alternatively, you could choose a more appropriate rate of loss, like 0.5kg per week.
  • heybales
    heybales Posts: 18,830 Member
    edited March 2021
    "If every day were like today, in 5 weeks...."

    You are going to make that happen for 35 days?

    Only if you could make reality match what is on paper, meaning you did exactly the level of activity that MFP thought you would do, and you ate the same deficit each day, and were totally accurate on both sides.

    Every day cannot possibly be like today, in reality.
    The estimate of what you burned is not true - you may have selected sedentary and aren't, and burned more.
    You may have said you ate XXXX amount of calories, but really didn't.


    And BTW - a goal is something to be reached, not undercut like it appears you are making your eating goal which is max deficit - whether that is smart rate of loss or not.

    How about you get to within 5 kg of goal weight and say close enough, I'll stop there. Desire to do that?
    Probably not - then don't undercut your eating goal which already may not be reasonable.
  • kenyonhaff
    kenyonhaff Posts: 1,377 Member
    It's just an ESTIMATE. As others have said, there's a lot of variables that can change the actual outcome.
  • whoami67
    whoami67 Posts: 289 Member
    It's inaccurate because 1200 is the lowest calories. If you're smaller and need fewer calories, you won't have a big enough deficit at 1200 to lose 2 lbs per week. You need to be in a deficit of 500 calories a day to lose 1 lb a week; 1000 calories a day to lose 2 lbs. 1200 calories may not allow you to get that big a deficit, but MFP know that it would be (almost) impossible for you to be healthy on fewer than 1200 calories a day so it doesn't allow for that.
  • cwolfman13
    cwolfman13 Posts: 40,768 Member
    glh72 wrote: »
    Hi, I'm curious why the 5 week weight estimate (when you complete diary at the end of the day) sometimes seems wrong.

    I've set a goal of losing 1kg a week, so assumed if I take in less calories in a day than my allowance, my estimated weight in 5 weeks would be a loss of at least 5kg - but it's not always so.

    Yesterday for example I was 100 calories under, but my weight loss was only projected to be 3.5kg.

    It's annoying to think you're doing well then the app tells you you're not!

    Any idea why this is please?

    Because it's just a very oversimplified algorithm based on very simple math and assumes everyday is going to in fact be just like today and that everything happens linearly...none of which is true. Think about it...how can everyday be exactly the same?
  • glh72
    glh72 Posts: 2 Member
    Sure yes I understand it's just an estimate and it's unlikely to be my exact actual weight in 5 weeks time - just wanted to know why MFP sometimes calculates that estimate incorrectly.

    But I think the explanation that MFP doesn't apply a calorie deficit below a certain level probably accounts for it (though I'm sure there are days when it does, but never mind) so thanks that helps.
  • sijomial
    sijomial Posts: 19,519 Member
    If you go to your set up and change it to "maintain current weight" temporarily you will be able to see if you actually have the headroom for that massive deficit without bumping into the minimum that this site will allow (1500 for males).