Hello,

Another approach:
Enter into E2:
=MATCH(1,B2:$B$65536,)+1
Enter into E3:
=MATCH(1,INDEX(B:B,E2+1):$B$65536,)+E2
Copy down until you see error values...

Calculation times for 2000 rows with 115 "one"s: 0.65 millisecs
[Max': 48.77 millisecs where column D took 45.48ms]

Regards,
Bernd