Right,
I had the same preponderance, and there are a number of ways you can calculate a number.. pick one..:)
But seriously its a waste of time, the reason you want a stash is to generate income... If you have an income (I.e likely pension payout) there is no value in back calculating it to NW.
I.e you need $1M to generate $40k.. Lets say you have a pension that projects $20k.. if you need $40k to live, well now you only need a stash of $500k... that's the only useful comparison.
OK, so your inner Scrooge is still not satisfied?.. OK take the value of the annual pension in x years time.. now multiply that by 25 (4%)rule... Thats the extra future net worth.
so lets say you have $32,000 a year.. multiply by 25 =$800k
But what is that worth today?.. lets do some sample numbers.. you can put in your own.. Lets say you have $800k in 5 years time.. and x is the value in todays dllars assuming a 3% inflation.
so x*(1.03)^5 = $800k
1.03^5 = 1.159
so x = $800k/1.159 = 690k.
As they say "close enough for government work"