bi-monthly and / or extra toward principle?

If I borrow, say $50,000 for 15 years at 4.74%, what makes for the quicker payoff? Paying monthly but adding approximately $122 to the payment to make it an even $500 per month rather than $388 or making twice monthly payments of $250 each? I can’t find a loan calculator that shows the difference of paying additional but bi-monthly.
Thanks for your help. I always like it when you’re on Channel 9 with your good advice!

Terry Says:  Here’s a great calculator to help you figure that out!  You can input different payment amounts and also different payment frequencies.  Let me know what you decide!