Figuring push time

[coops]

I am just getting my feet wet with developing my own film, and want to push a roll of Neopan 400 one stop, then another roll two stops. I am using Kodak Tmax rs to develop. I cannot find a formula to use to figure out how much longer I need to develop. A friend told me it's about 2 mins per stop, which at the temp I am developing at, takes me from 4:45 mins to 6:45 mins, and then 8:45 mins for the 2 stop roll.
I want to get this down before I try it with my 4x5's.

Thanks

[Paul Bujak]

Check the Massive Dev Chart at www.digitaltruth.com. Click on your film and developer in the drop-downs and there are the development times. I find them good for starters.

[coops]

Thanks, lots of good info there. I used the suggested times, and while no way close to being proficient at determining the quality of a negative, the roll shot one stop under looks good, with lots of contrast. The first 4 rolls I shot and developed looked really flat and dull. Hopefully these will be better.
Cheers