Elon Musk says Twitter is now worth less than half of what he bought it for -- and, if you'll recall, that was like $44 billion ... so, yeah, a BIG drop-off indeed.

The Chief Twit made the new valuation in a company-wide email he sent to remaining employees -- this per the NYT, which says it got its hands on a copy. In the internal memo, EM says Twitter is currently worth $20 billion ... $24 billion less than his purchase price.

While that may seem abysmal, Elon actually told his workers that -- for a time -- things were at risk of being much worse after he took the reins ... explaining Twitter was 4 months away from running out of money and going bankrupt at one point over the past several months.

In his note, he reportedly goes on to say that "radical changes" he's imposed were necessary to save money -- including the mass layoffs and other cost-cutting measures (i.e. auctions, etc.). The Times reports EM also said Twitter should be looked at as an "inverse start-up."

Now, as for why he was spilling these deets to the Twitter fam ... the Times says he was explaining their new stock compensation package. Basically, Twitter employees will receive stock grants for the holding company he used to buy Twitter -- the "X Corporation" -- which will operate under the current $20B estimate. Workers will then be able to sell and cash in on their privately held stock every six months. His other company, SpaceX, acts similarly.