To me, the calculator looks off by a 10% factor or more.
It's expected value is higher of what I get on slush's pool, and since the pool is meant to get your throughput (almost) at the expected value, it's either something wrong with me and the pool, or an over optimistic calculator.
Also, I went mining for about 5 days, with an expected 3 days of payout, but I found nothing. But that sounded perfectly normal to my ears.