Enter a recent 5K, 10K, or 15K result and get your projected half marathon finish time and pace, based on Riegel's race-time prediction formula.
This is an estimate, not a guarantee: Riegel's formula assumes your endurance, training volume, and race-day conditions carry over comparably from your shorter race to the half marathon distance.
A formula can tell you what's mathematically possible, but it can't tell you how to actually get there. RunLetters Half Marathon Coaching pairs you with a real coach (not an app) who builds your training around your predicted time, adjusts the plan as your fitness changes, and is in your corner from week one to the start line.
See the coaching program