Home Equity line of credit calculation

[Steve Tse]

Hi there, great minds of BPs. Curious to know if someone has a good way to calculate the monthly payment on HELOC. For example, if I have 300k credit line at 3% interest for 10 years. I can derive that my monthly payment on interest only would total to $750 (300,000 x .03)/12

What would be the simplest way to calculate monthly payment on interest and principal ? 

Am I right to assume that the principal only payment be $2500/month (300,000 / 120) so principal & interest per month would total $3250 (750 + 2500) ?