You do realize that with current US interest rates the interest on a 21 day hold would amount to even less than $150[1] per $1mil held - and thats assuming that

You do realize that with current US interest rates the interest on a 21 day hold would amount to even less than $150[1] per $1mil held - and thats assuming that they could even get Fed Reserve lending rates, which you're not going to be getting from your bank no matter how much money you have with them [2]. Given that that amounts to less than $2600/yr - with that massive assumption that PayPal can even get that rate of interest, do you think that they're really doing it for what amounts to a rounding error for a company that size, or is it, maybe, just about possible that their operational risk might run close to that number as well? [1] $1mil * 1.0025^(21/360) = 145.6 - assuming A/360, $143.6 with A/365 [2] Current US interest rate is 0.25% - but that's the rate at which banks can borrow from the Fed, not the rate that you'll get from your bank.