42cal logo
42cal
MarathonOS

Run Your Next Marathon.

Free Training Tools

View all →

Pace Calculator

Calculate splits, finish time, and pace for any distance.

Race Time Predictor

Predict marathon, half, and 10K times from a recent race.

BQ Calculator

Check if your time qualifies for the Boston Marathon.

Training Pace Zones

Get your VDOT and five training zones from Jack Daniels.

Race Day Fuel Planner

Plan carbs, hydration, and electrolytes for race day.

Course Difficulty Analyzer

Score any course on elevation, altitude, heat, and more.

MarathonOS

An iOS app for marathon training. Track runs, follow a plan, prepare for race day.

Join waitlist →

42Cal · MarathonOS

© 2025 42Cal. All rights reserved.

Tools

Your Race HistoryRace Time PredictorCompare RacesBQ CalculatorPace CalculatorTraining PacesDifficulty AnalyzerFuel PlannerAll tools

Explore

BlogLocationsDistancesCountries
SupportPrivacyTermsFeedback: biz@42cal.com

    Featured Races

    Aug 22, 2026Marathon (26.2 miles / 42.2 km)
    The Lowdown

    The Björn Borg Helsinki Marathon builds on the long tradition of the Helsinki City Marathon, an established August classic that has drawn international runners since the early 1980s. Rebranded with strong sponsorship, the race retains its reputation as a well-organized urban marathon that showcases Finland’s capital in late-summer light. The event attracts a mix of local clubs, recreational runners and international visitors seeking a scenic, fast course and a relaxed Nordic race experience. The organizers emphasize sustainability and runner services, with plentiful aid stations, pacers and post-race festivities that celebrate Helsinki’s outdoor café culture. The course threads together Helsinki’s most photogenic waterfronts and green spaces, offering sustained views of the Baltic shoreline, the tree-lined Esplanadi and the calm waters of Töölönlahti. Runners pass notable landmarks and cultural sites, enjoy long, runnable stretches on flat city boulevards, and take in seaside promenades and parkland that provide shade and refreshing breezes. The route is spectator-friendly, with lively fan zones, local bands and community support that create an upbeat, encouraging atmosphere from start to finish. Typical late-August temperatures are cool to mild, helping many runners target personal bests. The Björn Borg Helsinki Marathon is run on an AIMS-certified course and is accepted as a Boston Marathon qualifying event, making it appealing to those chasing qualifying times as well as first-time marathoners. Whether you come for a racing effort or to savor Helsinki’s coastal scenery and urban charm, the event delivers professional race logistics, warm local hospitality and a memorable summer marathon experience.

    Björn Borg Helsinki Marathon

    Helsinki, Finland

    Oct 11, 2026Marathon (26.2 miles / 42.2 km)
    7/10 CR

    MARATHON MÜNCHEN by Brooks

    Munich, Germany

    Article

    The Runner's Complete Guide to Race-Day Fueling

    “I tell our runners to divide the race into thirds. Run the first part with your head, the middle part with your personality, and the last part with your heart.”

    — Hal Higdon

    Nov 8, 2026Half Marathon (13.1 miles / 21.1 km)
    96m Elevation

    Garda Trentino Half Marathon

    Riva del Garda, Garda Trentino, Italy

    Sep 5, 2026Marathon (26.2 miles / 42.2 km)
    +1,496m Net Climb

    Jungfrau-Marathon

    Interlaken, Switzerland

    Oct 18, 2026Marathon (26.2 miles / 42.2 km)
    6.0K Runners

    IMT Des Moines Marathon

    Des Moines, IA, United States

    3K+
    Miles of Racing
    Ready to explore
    Oct 4, 2026Marathon (26.2 miles / 42.2 km)
    Mild Weather

    Run in Lyon Marathon

    Lyon, France

    Article

    Post-Marathon Blues: The Emotional Comedown After 26.2

    Nov 1, 2026Marathon (26.2 miles / 42.2 km)
    120m Elevation

    City of Oaks Marathon

    Raleigh, NC, United States

    “Run when you can, walk if you have to, crawl if you must; just never give up.”

    — Dean Karnazes

    Nov 22, 2026Marathon (26.2 miles / 42.2 km)
    25K Runners

    Philadelphia Marathon

    Philadelphia, PA, United States

    Oct 4, 2026Marathon (26.2 miles / 42.2 km)
    122m Elevation

    Maine Marathon

    Portland, ME, United States

    Dec 6, 2026Marathon (26.2 miles / 42.2 km)
    The Lowdown

    Our point-to-point, net-downhill course has remained unchanged for 42 years, starting from Folsom’s scenic foothills and ending at the historical California State Capitol. CIM has provided over 100,000 runners of all speeds–from first-timers to the fastest of the fast–the best chance to achieve their marathon goals.

    California International Marathon

    Sacramento, CA, United States