Iron Man has already proved to be pure gold for Marvel Entertainment (NYSE:MVL). But if history serves, the film is about to go platinum by netting more than $300 million at the domestic box office.

Here's why:

Film

31-Day Total

Total

Difference

Spider-Man

$353.8

$403.7

$49.9

Transformers

$290.4

$319.2

$28.8

Source: Box Office Mojo. Dollar amounts are in millions.

Through its first 31 days, Iron Man had accumulated $276.2 million nationally at the box office and $517.6 million worldwide.

With weeks to go before the film is pulled from theaters -- both Spider-Man and Transformers spent at least four months on the big screen -- the $300 million plateau is all but guaranteed, which means Marvel executives will very likely raise guidance and send the stock soaring.

Let's revisit the numbers. Marvel said in a 2006 presentation that a $300 million film would return $222 million to the company in operating profit before merchandising. Of that, executives estimated that 23%, or $51 million, would be realized in the year of release.

To be fair, Marvel also said recently that costs could trend incrementally higher than anticipated in 2006. Still, executives call for between $104 million and $122 million in net income in 2008 -- or $1.35 to $1.55 per share -- for just the core business. Not a penny of expected film profit is included.

Crazy, right? I'll say: $51 million taxed at 39% is $31.1 million. Per-share, that comes to $0.40. Forty freaking cents without any contribution from the forthcoming reintroduction of the Hulk to celluloid.

It is possible, of course, that revenue won't be recognized in 2008. The DVD selling season could slip. Management could fail to contain costs. A stray butterfly in the Amazon could cause a hurricane in Manhattan.

Nevertheless, I'm optimistic. Consider the competition, or lack thereof. Disney's (NYSE:DIS) sequel to the Chronicles of Narnia isn't performing to expectations. Speed Racer has been a bust for Time Warner (NYSE:TWX). And while Indiana Jones and the Kingdom of the Crystal Skull has the makings of a blockbuster, it, like Iron Man, is distributed by Paramount Pictures -- good news for parent Viacom (NYSE:VIA).

Finally, there's Sex and the City, which is whipping up plenty of interest among fans like my wife and has the makings of a hit. But let's be honest: Sex's viewers aren't likely to spend a sawbuck to see ol' Shellhead.

Thus I'm sticking with my math: Marvel will earn at least $0.40 more than current estimates suggest, which means this super-powered stock trades for no worse than 20 times current-year earnings.

A platinum-plated bargain? No. But not at all expensive for a business whose returns on invested capital are -- wait for it -- more than three times better than entertainment top-dog Disney.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.