Training · Free tool
Training Start Date Calculator
Pick your race day and the length of your training plan. We count back to the exact date you need to start, and show how many weeks you have until the race.
How long should a training block be?
Most marathon plans run 16 to 20 weeks; half-marathon plans 10 to 14; a 10K block 8 to 12. The right length depends on where your fitness is now. If you are already running consistently, the shorter end is fine; if you are starting from a low base, give yourself the longer build — and a few weeks of easy running before the plan even begins.
Counting back from race day is the planning step runners most often skip, then discover six weeks out that they are behind. Fixing your start date now means every long run and taper week lands where it should.
What if the start date has already passed?
If counting back lands you in the past, you have three options: pick a shorter plan, choose a later race, or compress the schedule and accept a more conservative goal. Cramming a 20-week build into 12 weeks is how injuries happen — when in doubt, shorten the goal, not the ramp.
Already have a solid base of weekly mileage? You can start later than a beginner and still arrive race-ready, because you are not spending the first month just building back to a runnable volume.
Frequently asked questions
When should I start training for a marathon?
For a typical 16-week plan, start training 16 weeks (about four months) before race day. Enter your race date above and the calculator gives you the exact start date.
How many weeks before a half marathon should I train?
Most half-marathon plans are 10 to 14 weeks. Choose your plan length above and the tool counts back to your start date.