Setting calorie goal weight loss post menopause

I don't think you have messed up your metabolism. Those calculators only estimate your TDEE at best. You have done very well going by observing what your maintenance is by looking at your own numbers. My only advice would be to make your calculations based on a longer period - 4 to 6 weeks as 1 week is too short a period and is marred by fluid fluctuations.

If you set yourself to eat 250-300 cals less than your maintenance (as you observe it to be) that sounds like avery nice pace of weightloss and quite sustainable.

My personal numbers are 5'7, 160 lbs and I maintain at 1600 cal on average (if I don't count any steps or exercise what so ever).

Again the best you can do is make an estimate and it isn't even that important if your maintenance is 1600 or 1700. If you aim for 1500-2000 calories weekly deficit it would be very good. Don't get sucked in by exact calculations.

Good luck. Don't lose patience.

I'll start with the TL;DR, purely from my experience and opinions: Logging experience over 4-6 weeks or so gives a better personalized estimate of calorie needs than any calculator or even fitness tracker. If your multi-weeks show you maintaining on 500-1600 calories with no significant change before or during in eating style or exercise/job exertion activities, I'd believe the results. Slow weight loss with a small calorie deficit is pretty painless, but in some ways takes even more patient persistence than a more rapid weight loss.

At more length:

The calculations are just statistical estimates yielding the average calorie need for demographically similar people. Most people will be close to average, but a few can be surprising far off. That's the nature of statistical estimates. For example, both MFP and my good brand/model fitness tracker (one that others here say is close for them) give me estimates that are about 25-30% off from what I observe in 9+ years of quite consistent logging experience. That's rare, but it can happen.

As a bonus, using your own logging and weight-change history compensates somewhat for any patterns of logging imprecision that may be happening. (That's not a diss: Logging is a form of estimating, too. Getting a workable estimate matters, so it's good to use consistent habits, after the initial learning curve settles down.)

When I needed to lose a few pounds that had crept on in roughly the first 4 years of maintenance, I decided I didn't want to deal with a significant deficit. I decided I'd eat that 200-ish or so number of calories under maintenance that you're talking about, and I honestly didn't always stick with that every single day. Over the course of a year or so, I lost maybe 12ish pounds . . . verrrrrryyy gradually. Back-calculating my actual average deficit, it was probably more like 100-150 calories daily because of the days I didn't stick with the full 200 or so deficit, or even ate over maintenance occasionally.

The big plus: Almost entirely painless. One minus: It can take a long time to show up on the scale, amongst the routine daily multi-pound fluctuations in water retention and digestive contents. There was even a period of about 4-6 weeks where my weight trending app thought I was maintaining or even gaining a little, but I was pretty confident - based on experience - that I was in a deficit, so I plowed on. Sure enough, the scale drop I expected showed up eventually, and rather suddenly. Go figure.

I'd do it again that way, with a similar amount to lose. It will also work for larger amounts to lose, but it does require consistency, persistence, and faith in both one's logging habits and calorie needs.