The use of two m's to denote millions is becoming less common. Frequently, in finance and accounting settings now, an analyst will use k to denote thousands and a capitalized M to denote millions. For example, $100k x 10 = $1M.

Abbreviating one million dollars is done using the above abbreviations. Generally, the abbreviation with two M's is preferred in finance. So a million dollars is written as $1MM.

M is the Roman numeral for thousand and MM is meant to convey one thousand-thousand — or million. To take it further; one billion would be shown as $1MMM or one-thousand million.