Marathon Training Calculator
Plan your marathon buildup by calculating a weekly mileage target and ideal training paces from your goal finish time. Use it when structuring a training block weeks before race day.
About this calculator
This calculator estimates a target weekly mileage figure by relating your goal marathon time to your current fitness base, the runway you have before race day, and your experience level. The core formula is: result = ((goalTime / 26.2) × currentWeeklyMiles) / (weeksToRace × experienceLevel). Dividing goalTime by 26.2 converts your overall finish time into a per-mile pace proxy. Multiplying by current weekly mileage scales the output to your present training volume. Dividing by weeksToRace spreads the workload across your available training window, while the experienceLevel factor adjusts for how efficiently a more seasoned runner can absorb mileage. The result guides how much weekly volume to target at this point in your plan, helping you progress safely toward race fitness without overreaching.
How to use
Suppose your goal time is 240 minutes (4 hours), you currently run 30 miles per week, you have 16 weeks until the race, and your experience level is 1.2 (intermediate). Step 1: divide goalTime by 26.2 → 240 / 26.2 ≈ 9.16. Step 2: multiply by currentWeeklyMiles → 9.16 × 30 = 274.8. Step 3: multiply weeksToRace by experienceLevel → 16 × 1.2 = 19.2. Step 4: divide → 274.8 / 19.2 ≈ 14.3 miles. This figure represents your adjusted weekly mileage target for this stage of training.
Frequently asked questions
How does experience level affect my marathon training mileage target?
Experience level acts as a divisor in the formula, so a higher value lowers the calculated weekly target. This reflects the fact that seasoned runners have better aerobic efficiency and can achieve race fitness with relatively less raw volume. A beginner (level 1.0) will receive a higher mileage prescription to build the aerobic base they lack, while an advanced runner (level 1.5+) gets a more conservative number because their body converts training stimulus more effectively. Choosing the right experience level is therefore crucial to avoiding both under-training and injury.
What is a safe weekly mileage increase when training for a marathon?
The widely cited guideline is to increase weekly mileage by no more than 10% from one week to the next, often called the 10% rule. This conservative progression limits the cumulative stress on bones, tendons, and connective tissue, which adapt more slowly than cardiovascular fitness. Most structured marathon plans also include a cutback week every third or fourth week where mileage drops by 20–30% to allow fuller recovery. If the calculator's target feels like a large jump from your current volume, phase in the increase over several weeks rather than jumping straight to the recommendation.
How many weeks before a marathon should I start structured training?
Most coaches recommend a dedicated training block of 16 to 20 weeks for a first-time marathoner, and 12 to 16 weeks for experienced runners who maintain a solid base year-round. The longer window allows gradual mileage buildup, multiple long runs of 18–22 miles, and adequate taper time in the final 2–3 weeks before race day. Starting too close to the race forces aggressive mileage jumps that elevate injury risk. If you have fewer than 10 weeks remaining and your current weekly mileage is below 25 miles, consider targeting a later race to allow proper preparation.