It would be helpful if it were possible to check on personal stats tab how much satoshis have been wagered on the account so far.
If you've never claimed a bonus before you can see how much you have wagered on the site by going to the multiply tab. At the top of the page you'll see a message: "You are eligible for a bonus of x.xxxxxxxx BTC for playing MULTIPLY BTC! Click here to claim your bonus."
For every 100 satoshi you wager on dice or betting, the bonus you are eligible for increases by 1 satoshi. So, multiply the bonus you are eligible for by 100 to see how much you've wagered in total on the site. Again, this will only work if you've never claimed a bonus before.