BMR can NOT truly be calculated online

I don't think I have ever seen anyone on here say that BMR calculators are 100% accurate. Ever.
I do think it is a starting place. One could do the same thing you did but use a online BMR calculation as a basis to figure TDEE and use that as a starting point, though I would suggest giving it more than a few days.

I do agree that people need to understand that these calculators, along with calorie burned calculators (including HRMs) are estimates.

ETA - I also think in a lot of cases people gain weight/fail to lose is not that the BMR numbers are wrong.

I guess the only difference I see between picking an arbitrary number, like 1200, and adjusting up and down and using an online calculator to estimate BMR, then figure TDEE and adjust from there is at least the BMR/TDEE calculator is more accurate for a larger percentage of the population. And there is less chance of having too great of a deficit.

An online calculator may not hit the bulls eye but for a lot of people it'll get them relatively close.

Exactly why most of us that recommend using BMR and TDEE to work out what you need will tell you to adjust down 100 calories or so after a few weeks if nothing happens.

Forget about bmr or bmi
Just stand in front of mirror if you are satisfiyed that's it. otherwise change your body shape.

Totally this!!!

The problem is people don't know HOW to do it!

Sounds like another thread trying to get support for people undereating--sorry, I don't buy it. IF you need to eat 1200 (or fewer) calories to lose weight then you should probably get your hormone levels checked or reconsider your plan. Yes, BMR may be quite off but BMR is only 1 such factor in determining your TDEE. TDEE minus 15-20% is the preferred way to estimate your calorie target and then adjust as needed. Starting off at some arbitrary number that you THINK is right could lead to undereating straight off the bat and the hormonal implications of doing so are such that you might lose X amount of weight despite having a deficit that SHOULD lead to X + 1 pound (just as an example)...but you wouldn't know that because all you have to go by is the number on the scale. Better to eat slightly more (using the TDEE approach) and monitor the effect then adjust as needed. Just my opinion though.

Exactly. This. All of this.

I started my diet at 1200 for a day or two and upped it 100calories per day until I found where I maintain weight. To lose I just subtracted some from that, upped my exercise, and ate back my exercise calories almost every time.
P.S. BMR and RMR are not the same either.

1200 is just 'a number' that MFP gives everyone. If you are small of stature or older then yes maybe it IS right for you but you have to figure it out not just 'pick' at random. MOST people are NOT small of stature and / or seniors. Before I tell anyone to eat more I LOOK at the stats that I can see on their profiles - of course if they haven't bothered to fill anything out then I just ignore them because they OBVIOUSLY have no desire to have input.

Anyone who tells people that they HAVE to eat over 1200 calories WITHOUT KNOWING ANYTHING ABOUT THEM has not understood the concept of BMR/TDEE - 1200 CAN BE FINE for people who are small, short, old, have had surgery, have other issues. There is no way to know without having some information.

Your logic is flawed--the most acceptable LOW POINT is going to cause hormonal changes that will skew the scale number. Dieting and super high deficits = higher cortisol = more water weight = less weight LOST on the scale than is actually true = distorted picture of your true TDEE = further undereating when you could eat more and get results.

I think you have a good idea but I'd rather start the other way around--with the highest acceptable number and see how close it comes. Then adjust. You're not going to gain any significant amount of weight in 2-4 weeks.

How do you figure? If someone has a BMR of 975, or an RMR of around there lets say, then 1200 is above their low point. Also, if your RMR is 975 how is 1200 a "high deficit" smh. That is flawed. Plus, as I said, the point is that people should be able to do as they wish because they know what works for them better than anyone else usually.

Not true. Most people have NO IDEA how the human body works. They don't know the hormonal repercussions of undereating, they don't know that a low fat diet wreaks havoc on the endocrine system, and they don't know that weight loss isn't linear. In your theoretical example, yes they'd be fine with the LOWEST acceptable minimum but that's rather rare for someone to have a BMR of that low. So--it could be okay, but it would work for the exception rather than the common person.

Bottom line is no one is making any one do any thing. You ask a question, 40 people give advice. This is where common sense and thinking for yourself comes in. People on here get stuck on 1200 calories as a number to worship because the calculator only goes down to 1200. No matter what ridiculous idea you have on weight loss it won't give you less than 1200.

If you have no idea what you're doing or should be eating using the calculators CORRECTLY will at least give a guideline to start with. If you take BMR as your bottom basement never eat below that number and your TDEE as your ceiling never eat above it number then you can start playing in the middle. See what works and it takes weeks to find out if any particular number is working not a couple days of trial then bounce off to another number.

There are way too many factors that play into the whole numbers game. Most people perceive themselves as far more active than they are and tend to over estimate exercise and under estimate what they eat so the numbers are screwed up right off the bat.

If you stick with it long enough you start to see how it all works for YOU but most people have the idea that they'll go on a diet, eat next to nothing, be slim and sexy next week and it's all good now. The first thing that needs to be adjusted before anyone worries about numbers is your head. You have to get your mind around the fact that you go fat over a period of time by doing what you were doing. You can't reverse it over night and you'll have to maintain your new eating habits for life. For a lot of people the brain just isn't in the right spot and it never happens.