Pick your race, how many weeks you have and what you run now. The builder raises your weekly miles by about 10% at a time, makes every 4th week easier and tapers before race day. It's general guidance, not medical advice: check with your doctor before you ramp up, and adjust when your body says so.
The structure paid apps charge for, free: pick your race, your weeks and where you are now. You get a week-by-week plan with build weeks, cutback weeks and a taper. General guidance only; check with your doctor before ramping up.
Want the full explanation? Read our 16-week 50K plan guide, and check the gear you'll need: GPS watches, hydration vests and headlamps.