I'm fairly new here, so forgive me for resurrecting this old thread. I'm also in the DC area (Fairfax City to be exact). It sure can be hard to be mustachian with the housing prices in this area! I see lots of posts of people saving 60%+ of their takehome pay, and I wonder how that is possible with a DC mortgage :)
Different people look at it different ways, but it seems entirely reasonable to me to count any amount of your mortgage payment that is going to principal as part of your savings rate.
Anything adding to net worth can theoretically be counted as savings.
For example, let's say that over the course of 1 year you make $80,000. You start with 40k in credit card debt. No other debt (no mortgage, no student loans, etc.). Your net worth is -40k. Let's say over the course of the year you spend 40k on expenses (rent, taxes, food, etc.) and pay down that 40k credit card bill to 0. At the end of the year, you have a 0 net worth.
IMO, you "saved" 40k that year of your 80k, for a 50% savings rate. Sure, you don't have any in the bank or any investments, but whatever your net worth went up by (excluding interest earned), one could view as savings. And if you continue to do that the next year, year 2, you would have 40k in the bank, and have spent 40k, for a savings rate of 50%. If year 2 is a 50% savings rate, why wouldn't you count year one as the same?
With that vein of thinking, if you have a large D.C. mortgage and spend 2,500/mo (or whatever) on your mortgage payment, and 500 of it goes to principal, count that 6k/yr as "savings" towards your savings rate.
It's equity you can tap and access (in the form of a HELOC or by selling and downsizing when you FIRE).
I don't personally do this, but I do think it's a completely valid way to look at things.
