Fartlek Pace Calculator Formula

Understand the math behind the fartlek pace calculator. Each variable explained with a worked example.

Use the Fartlek Pace Calculator

Formulas Used

Average Pace

average_pace = round(avg_pace * 100) / 100

Total Time

total_time = round(avg_pace * total_distance_miles * 10) / 10

Fast Distance

fast_distance = round(total_distance_miles * fast_fraction * 100) / 100

Easy Distance

easy_distance = round(total_distance_miles * (1 - fast_fraction) * 100) / 100

Variables

VariableDescriptionDefault
total_distance_milesTotal Distance(miles)5
fast_pace_minFast Segment Pace(min/mile)7.5
easy_pace_minEasy Segment Pace(min/mile)10
fast_fraction_pctFast Running Fraction(%)30
fast_fractionDerived value= fast_fraction_pct / 100calculated
avg_paceDerived value= fast_fraction * fast_pace_min + (1 - fast_fraction) * easy_pace_mincalculated

How It Works

How Fartlek Training Works

Fartlek (Swedish for 'speed play') mixes fast and easy running in an unstructured or semi-structured format.

Formula

Average Pace = (Fast Fraction x Fast Pace) + (Easy Fraction x Easy Pace)

Benefits

Fartlek builds both speed and endurance in a single session. The unstructured nature makes it mentally refreshing compared to rigid interval workouts.

Worked Example

5-mile fartlek with 30% at 7:30/mile and 70% at 10:00/mile.

total_distance_miles = 5fast_pace_min = 7.5easy_pace_min = 10fast_fraction_pct = 30
  1. 01Fast fraction = 30 / 100 = 0.30
  2. 02Average pace = 0.30 * 7.5 + 0.70 * 10 = 2.25 + 7.0 = 9.25 min/mile
  3. 03Total time = 9.25 * 5 = 46.3 min
  4. 04Fast distance = 5 * 0.30 = 1.50 miles
  5. 05Easy distance = 5 * 0.70 = 3.50 miles

Ready to run the numbers?

Open Fartlek Pace Calculator