To estimate my end networth I have been using the return rates posted on the Wiki Destock page here:
http://wiki.earthempires.com/index.php/Destocking

Where it says these things:

"a DMBR will get about 5.2 million networth for each billion cash they have left over after switching to MBR"

"a TMBR will get about 6 million networth for each billion cash they have left over after switching to MBR"

"you get about 4 million networth for each billion cash of your stockpile as a Democracy" (private market no MB switch)

"about 4.5 million networth for each billion cash of your stockpile as a Theocracy" (private market no MB switch)

How are these return rates calculated and how accurate are they?

Well your private market make up is like so:

3 troops
2.5 jets
2.5 turrets
1 tank

Then you look at how much each costs for you, and factor in how much net each unit is worth.

I have a demo with maxed tech and it goes:
$118 troop
$157 jet
$172 turret
$480 tank
so (3 * $118) + (2.5 * $157) + (2.5 * $172) + ($480) = $1656.50
for
(3 * 0.5) + (2.5 * 0.6) + (2.5 * 0.6) + (1 * 2) = 6.5 networth

$1656.50 / 6.5 = $254.85 per point of networth, if I bought exclusively off my private. Of course it depends if your private is big enough.

So is this statement correct:
"you get about 4 million networth for each billion cash of your stockpile as a Democracy" (private market no MB switch)

Well $1,000,000,000 / 254.85 = 3,923,876 networth. So yeah that statement is a good approximation.

you can check the other ones by starting at the base price and then multiplying in all the factors to see what the prices would be for those and then doing the same thing as in the above post

Thanks Blid, I figured it was something like that but I got a slightly different answer cause my tanks are at $482 @ 82% military tech. Pretty accurate then if you jump off your private only.

as a Demo you shouldn't be buying anything but troops, tanks and maybe jets off of your private. Typically public prices can be better then turrets until the last day.

Very true Andrew, but I am finding it very difficult to estimate the public market return.. I use my private market as a minimum estimated end networth. The estimate becomes closer I figure as public market prices rise up to my private market prices.