One of the most common mistakes first-time marathon runners make is getting the taper wrong. Some people cut their training too much and feel flat on race day. Others keep training too hard and arrive at the start line tired. The goal of a taper is simple: reduce fatigue while maintaining fitness. When should you start tapering? Most marathon tapers last 2–3 weeks before race day. A common structure looks like this: 👉 3 weeks out: reduce mileage by ~15% 👉 2 weeks out: reduce mileage by ~25% 👉