20-Week San Antonio Marathon Training Plan

The 2026 San Antonio Marathon is scheduled for December 6, 2026, so the 20-week window opens around July 19, 2026. Treat that as the outside edge of the window, then line week one up with the plan's normal weekly rhythm.

Use the longer window to make the early build calmer, not to add five months of hard training. The plan should begin close to your current load, hold most running easy, and delay the biggest race-specific work until the middle of the cycle. The course does not change the opening load you can handle, so choose from your current mileage and recent longest run before adding race-specific terrain.

Build general durability first. Add the race's hills, flat sustained running, downhill exposure, heat, or humidity in layers after the weekly rhythm is stable, then make the final long runs the most course-specific. Humidity is the first thing to train for. A December start near 61F with 86% humidity sounds mild and doesn't run mild, because sweat won't evaporate and your effort at any given pace sits higher than the thermometer suggests. Rehearse your fluid and sodium plan in humid conditions, not just warm ones.

Do not double weeks or cram missed mileage into the remaining calendar. Use your current mileage, recent longest run, experience, goal, and available days to choose a plan that can enter at an appropriate point while preserving the taper.

No, and that's the most common mistake runners make about it. The loop climbs 909 feet and descends 902, running between 622 and 814 feet, for a net change of about seven feet. Nothing is steep, but the constant rolling adds up and the bill arrives after mile 20.

Warmer and much stickier than most winter marathons. Race morning norms are near 61F with 86% humidity, an average high of 66F and an average low of 44F. Humidity rather than temperature is what slows people here, because sweat stops evaporating and perceived effort climbs at any given pace.