You do not need a spreadsheet: https://help.steampowered.com/en/accountdata/AccountSpend
In case anyone is wondering, Steam updated their back-end in 2015. So "OldSpend" is everything pre-2015 and "TotalSpend" is everything including post-2015.
Never been more scared to click on a link.You do not need a spreadsheet: https://help.steampowered.com/en/accountdata/AccountSpend
Its not the correct sum if you've bought games through trades by buying off CS:GO keys with real money through real people as steam friends. A lot of people used this to buy games in the third world.
My Total Spend is $180.49 but iam sure its not even close to the amount i've spent since i bought games by buying of CS:GO keys through real money and through real people.