I wouldn't get too hung up on BMRs. Unless you are hooked up to a laboratory machine all other methods are approximates.
The same is true with exercise machines that read out how many calories you are burning etc.
I've run into the ground two exercise bikes and currently working hard on the third one. Although I work out at the same rate on each of these bikes; each has given me a vastly different rate of calorie burn.
It is only through experience that I've learnt that if I work out at certain intensities (within myself - each bike's "intensity levels" are different), for certain amount of times and what time of day what I could expect on the scales as a result.
Also don't forget that BMR is a measure at rest ie how much energy you would just laying in bed all day.
How active you really are can make all the difference yet again.
Having said all that most responsible experts recommend weekly weigh ins.
My practice however was (and is) it weigh every day.
Doing so greatly aided my understanding how my body reacted to different forms and intensities of exercise, the natural rhythm of the body, how sleep affects weight loss, how sickness effects weight loss, how muscle making effects weight loss, how different foods and portions affects weight loss and above all kept me intensely aware of my weight loss mission and made sure that I was accountable for my actions - daily.
But daily weigh ins are not for the faint hearted. It quickly shows you just how much your body's weight can fluctuate from day to day.
But if you stick to it and don't live or die on the daily number you can learn an awful lot of useful things that will help you succeed.
My daily weigh ins mattered but it was my weekly weigh ins that counted as "solid" numbers for my journey's success.
My whole week's actions were focussed on getting a good outcome my weekly weigh in (each Friday).
One of the things that I regret not doing that you may find helpful is not only doing a weekly weigh in but also a weekly measure.
On the weeks that no noticeable loss is occurring (which will happen specially at the pointy end of your weight loss), you can take solace in shrinking waistlines, necklines and thighs etc.
The weeks when no weight loss is registering on the scales are usually the very weeks when muscle growth is kicking in.
Muscle that is making trimmer, more fit and upping your metabolism burn rate.
Hope you find this useful.