If you are leaving something in the tank your 1RM may be more. Also calculators like that tend to be more accurate the closer to 1 you plug in for the number of reps. 5 and below usually give a pretty good estimate but once your rep count gets up into the 6-10 range the estimates become progressively more problematic.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1