hi julie, is it a stationary bike? if so, plop it in front of the tv and peddle away to your favorite show. if not, you could easily bike 3 miles in 20 minutes or so. it would take me about 70 minutes to walk it. the thing is to just do something every day to get your blood pumping and your brain cleared out. those weekend warriors who push themselves end up with injuries. slow and steady wins the race. good luck julie......btw is a stone 14 lbs?