Boston Marathon
The oldest annual marathon. Cool spring conditions, qualifying-only field, downhill quad-trashing first half, Newton Hills back half.
The Quick Answer
Boston is cool but not low-sodium. Your sweat sodium concentration is fixed, so salty sweaters still need 700 to 1000 mg per hour even at 50F. Target 16 to 20 oz of fluid per hour, resist overdrinking in the downhill first 10 miles (the leading hyponatremia cause here), and pre-dose 600 mg sodium 60 minutes before the start.
Course Profile
Where The Sodium Math Bends
Schematic profile · Cramping windows tend to cluster around major climbs and the descents that follow them
Climate Window
40-65°F · moderate humidity
Climate
cool
Humidity
moderate
Cutoff
6h after final wave start
10-yr avg high
58°F
10-yr avg low
39°F
Record high / low
82° / 30°F
Years with rain
70%
Why This Race Is Hard For Sodium
The Cumulative Deficit Window
Boston is a cool-weather marathon where the standard advice ("you need less sodium when it is cool") is wrong for a large fraction of the field. BAA qualifiers are typically lean, well-trained, and high sweat-rate athletes. Many of them are also salty sweaters. The Newton Hills late in the race (miles 16 to 21) are where sodium-driven cramping most often hits, particularly the climb up Heartbreak Hill. Most athletes overdrink water in the first 10 miles when they feel cool, then run a sodium deficit into the back half.
Key Considerations
- Salty sweaters should treat Boston like a warmer race for sodium intake. Cool ambient temperature does not lower sweat sodium concentration.
- The downhill first 16 miles is deceptively heat-generating; quad work raises core temperature regardless of air temp.
- Hyponatremia risk is real at Boston due to ambitious mid-pack runners drinking aggressively in cool weather. Stick to fluid targets.
- Pre-race sodium loading the night before (salty dinner) supports plasma volume before a cool-weather start when thirst signals are blunted.
Finish Times
Who Finishes, And How Fast
Official 2026 results
Men winner · 2026
John Korir
2:01:52KEN
Women winner · 2026
Sharon Lokedi
2:18:51KEN
Finish rate ~97%
Go Deeper
See The Full Boston Strategy Playbook
Course segments, pacing bands, and a race-day execution guide.
Plan the five systems
Free Tools, Pre-Filled For Boston
Tap any tool. We pre-load your event, climate, and sweat profile. Adjust your weight and finish target and the plan generates instantly.
Sodium plan
Per-hour sodium and fluid targets for Boston conditions.
Carb fueling
Hourly carb targets and a fuel menu calibrated to your weight and the Boston duration.
Heat protocol
10-14 day adaptation plan if you're racing into a warmer climate.
Hydration audit
Weigh-in test that converts a 60-minute training session into a measured sweat rate.
Caffeine timing
Pre-race dose, mid-race top-ups, and race-week taper protocol for Boston timing.
Related Reading
Dig Into The Science
Sodium Calculator for Endurance Athletes (Free Tool)
Sweat sodium varies 3 to 4x across athletes. A free sodium calculator that sets an hourly target from your body, sweat history, and race-day climate.
Why Endurance Athletes Need More Carbohydrate
Carbohydrate is the limiting fuel for endurance. Why glycogen runs the show, grams per hour by duration, and how to train your gut to take more.
Your Boston Plan,
Built From Real Data.
Pro unlocks: distribution of sodium intake per hour for sub-3, sub-3:30, and sub-4 BAA finishers, your historical April long-run sweat rates from Strava, and a mile-by-mile schedule that pre-doses for the Newton Hills.
- Measured sweat rate from a Strava ride or weigh-in test
- Per-leg sodium schedule keyed to the course profile
- Multi-event race calendar across the season
- Post-race feedback capture so the next plan is sharper
Per race
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Unlimited race plans, Strava connection, multi-event calendar.
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Common Questions
About Boston
Do I need less sodium because Boston is cool?
Not necessarily. Your sweat sodium concentration is a fixed individual trait. Cool weather lowers total sweat volume but does not change the mg per liter you lose. If you are a salty sweater, your hourly target stays high even at 50F.
When in the race should I take my pre-loaded sodium?
A 600 mg dose 60 minutes before the start, paired with 16-20 oz of fluid, supports plasma volume through the first hour. The first on-course intake should happen within the first 30 minutes of running, before thirst signals appear in cool conditions.
How much fluid should I take in cool Boston weather?
For most athletes targeting a sub-4 hour finish, 16 to 20 oz per hour is the working window. Resist the urge to drink at every water stop in the first 8 miles; cool-weather overdrinking is the leading hyponatremia cause at Boston.