How fast can mortgage interest rates increase in a month period? Is there a limit to how interest rates rise in a given period?

No.. the market does whatever the market wants to do.. there is no cap.. but that's the down side of building a home vs. buying one already built.. you are subject to the rates at the time your home is finished and you are ready to lock in.. rarely is a home finished on time or early,. so even if you were within 60 days of locking, it's very possible you would blow through the rate lock anyway.. .. I'm the preferred Broker here in Scottsdale AZ, and Arizona and California is my primary market. If you or someone you know is looking for financing options, feel free to contact me or pass along my information. William J. Acres, Lender411's number ONE lender in Arizona. 480-287-5714 WilliamAcres.com NMLS# 226347 / RPM Mortgage NMLS 1541014 / AZMB0121893

As said previously, rates can move and change as fast as the stock market. they've been straight up nearly 0.5% in the past 2 weeks. That could continue or turn around. Some lenders offer a longer lock, or a "float down" option if they change after your lock and close enough to closing. Good luck!