Cumulative frequency formula???

Im trying to show:

Duration Name cumulativeDuration
3 Kev 3
2 Kev 5
4 Phil 4
1 Phil 5
2 Phil 7
3 Jack 3
2 Ross 2
4 Ross 6
5 Ross 11
2 Ross 13

Basically I want a formula (or macro) to get a cumulative amount based on the name given. If you have any suggestions, please help.

Thanks, Kev

In C2 and down:

=SUMIF($B$2:B2,B2,$A$2:A2)