Flat (but up and down)
The Bank of America Chicago Marathon climbs 243 feet over its 26.2-mile loop and descends 242 feet. Among the World Marathon Majors, the six-race series that also includes Boston, London, Berlin, Tokyo and New York, no other course pairs its up and down that closely: Berlin's 241 feet of climb comes with 260 feet of drop, and Tokyo loses 322 feet against only 198 feet gained. New York comes closest to Chicago's symmetry, 966 feet of climb against 958 of descent, achieved by climbing roughly four times as much. Chicago is the only one of the six where gain and loss land within a foot of each other.
The race's own site calls the course "known for its flat and fast course," and credits it with seven world records and, in the organizers' words, "countless personal bests." That claim holds up better for balance than for outright flatness. The Running Channel and RunnersConnect both rank Chicago second flattest among the Majors, behind Berlin, and on the most widely republished elevation dataset its 243 feet of gain runs higher than Berlin's 241 and Tokyo's 198. First-timers hear "flat" and hear "guaranteed personal best" regardless. What the balanced profile buys a runner is a course with no long grinding climb and no long free descent to bank time on either, a narrower and more honest promise than the fastest course on the circuit.
Even those elevation figures carry less precision than they look. Findmymarathon, Runna and worldmarathoner all publish an identical 243 feet of gain for Chicago, one dataset republished three times rather than three independent measurements. RunnersConnect's own figure for the same course is 187 feet, and a "certified elevation data" number cited elsewhere for Chicago runs closer to 115. Those gaps come from method: GPS-derived elevation gain depends heavily on how the underlying data gets smoothed before publication. The ranking that survives all of them is a modest one, with Berlin usually edging Chicago, and 42cal has a first-timer guide to Berlin for anyone weighing the two.
The forecast is a coin flip, and 2007 proved it
Across the years with reliable weather records, Chicago's race-morning start temperature has ranged from 32°F (0°C) in 2009 to 72°F (22°C) in 2007. That is a 40-degree spread on the single number a runner checks while getting dressed, drawn from one city, one Sunday in October, across more than twenty editions. The afternoon high has swung wider still, from 45°F to 88°F. 42cal has written separately about what each degree above ideal costs a marathon finishing time, and Chicago's recorded range covers nearly the full scale that piece describes.
2007 is the year the range earned its reputation. The temperature hit a race-record 88°F by late morning, and organizers halted the course roughly three and a half hours in. Around 400 runners sought medical attention, more than 30 were hospitalized, and 10,934 registered runners did not finish, a DNF in race shorthand; roughly 10,000 more never started at all.
Where the data disagrees. A 35-year-old runner named Chad Schieber collapsed near mile 18 that day and died, and the race is still described online as having killed him with heat. The Cook County medical examiner found a different cause: mitral valve prolapse, a pre-existing heart condition, with no evidence of dehydration. The roughly 400 medical cases and the early course shutdown trace to the heat. Schieber's death, per the autopsy, traces to his heart.
2021 brought the warmest start since 2007, near 70°F, with the high reaching 79. 2023, the year Kelvin Kiptum ran 2:00:35, a time that stood as the marathon world record until London broke it in April 2026, started cold and still, at 46°F with little wind and a mostly cloudy sky. 2019 started in the low 40s with wind chills near 32°F. 2025, the most recent edition, landed in between: 50°F observed on the start line, against a forecast of 53°F. Training through one Chicago October means training for weather that has, within the last twenty years, sat at nearly every point of that 40-degree range.
Where the watch stops telling the truth
Chicago's opening and closing miles run between the same tall buildings that make it a striking city to run through, and those buildings play havoc with a GPS watch's signal. A satellite-based watch needs a clean line to the sky to measure distance accurately; downtown, the signal instead bounces off glass and steel before it reaches the device, an effect runners and course guides call an urban canyon. Canadian Running Magazine reports that most GPS watches are effectively useless by the time a runner reaches the first mile marker, and quotes Hansons Running, a coaching group that toured the course, telling runners flatly: "DO NOT USE ANY GPS DEVICE IN A MAJOR CITY FOR PACING PURPOSES."
Believe in the Run, another outlet that has run the course, found the same problem in the same stretch and advises turning off a watch's auto-lap feature entirely, lapping manually at each painted mile marker instead. Coach, quoting Chicago finishers, passes on the same workaround. Believe in the Run also notes that the course paints a blue line marking the certified tangent, the shortest legal path between the start and finish banners, which is the very line a confused GPS reading is failing to measure against. That means the pace number on a runner's wrist in mile 1, exactly when the temptation to go out fast is strongest, is often simply wrong rather than slightly off. 42cal's pace calculator is one way to plan target splits before race day, since the watch cannot be trusted to confirm them live through the Loop, Chicago's dense downtown core.
Where the crowd thins and the noise returns
Chicago draws roughly 1.7 million spectators across 29 neighborhoods, one of the largest crowds on the circuit and consistent with the 8-out-of-10 crowd rating in 42cal's race database. That crowd is not spread evenly. NBC Chicago, Coach and Believe in the Run each describe the same stretch, roughly miles 14 through 19, as where the course quiets down after leaving the Loop and runs through lower-rise neighborhoods with fewer people lining the route. The energy returns hard at mile 19 in Pilsen, where residents are known to set up their own aid stations, and again around mile 21 in Chinatown, with drums and lion dancers. The quiet stretch is not uniformly quiet: Believe in the Run calls mile 15, inside that same window, one of the loudest single blocks on the course, so the thinning reads as patchy rather than clean and predictable.
If it lands on a sunny year, that same low-rise western stretch is also where the shade runs out, according to Coach's panel of finishers, though that is the only source making the connection explicitly. Better documented is what comes after: Michigan Avenue, from roughly mile 23 to the finish, is a long straight run that Coach says "seems to last forever," and Believe in the Run separately confirms as the same straight shot into the line.
The 65 minutes between Wave 1 and Wave 3
Chicago starts runners in three waves rather than one mass field. Wave 1, which includes the elite runners and corrals A through E, numbered starting pens assigned by accepted qualifying time, goes off at 7:30 a.m. Wave 2, corrals F, G, H and J, starts at 8:00. Wave 3, corrals K, L, M and N, assigned by expected finish time rather than a qualifying mark, starts at 8:35, a full 65 minutes after Wave 1. There is no corral I in the official race day timeline.
That gap matters more than it sounds. On a warm-start year like 2021, when the temperature opened near 70°F and climbed to 79, a Wave 3 runner crosses the start more than an hour further into the day's warming curve, closer to the forecast high than the forecast start by the time they are a few miles in. The race does not publish that connection directly; it follows from the wave schedule and the weather record above.
Both the start and finish sit in Grant Park, at Columbus and Jackson Drive, with gear check open from 5:30 a.m. to 4:00 p.m. One logistics detail is worth knowing ahead of time: the race's own site warns that getting from the finish line to the 27th Mile Post-Race Party, in Butler Field, where alphabetical towers mark reunion points by last name, "can take 30 minutes or longer." Planning to meet at the towers, not the finish line, avoids a long search on tired legs.
Runners chasing a Boston qualifier, a finishing time under Boston's standard for their age and gender, can check a projected time against those standards with 42cal's Boston qualifier calculator. Chicago sets separate qualifying times for entry to its own race, which for 2026 ran from sub-2:50:00 for men 16 to 34 up to sub-4:50:00 for men 80 and over.
Getting in for 2027
Chicago's 2026 field holds 55,000 participants, with about a third running for official charities. The main entry routes for 2026 have already closed: the lottery, time qualifiers, legacy finisher status and the Chicago Distance Series alike. Two remain open as of this writing, both first-come and capacity-limited: official tour operator packages through August 16, 2026, and the charity program through September 15, 2026, which asks a $2,200 fundraising minimum on top of the standard entry fee. Confirmed for 2027: anyone who completes all three 2026 Chicago Distance Series races receives an exclusive medal and a guaranteed 2027 entry. A 2026 entrant who has to cancel does not get an automatic deferral. The race's FAQ states plainly that no deferrals are allowed for a participant cancellation, and the only path to guaranteed entry the following year is applying fresh and paying that year's fee.
What has not been confirmed yet is anything about the 2027 race itself. The official application page carries no 2027 dates as of this writing and points visitors to a newsletter signup instead. Some secondary sites guess the window will open in late October 2026, extrapolated from the 2026 race's lottery, which opened October 21 and closed November 18 of 2025, a guess based on a single prior year rather than a published date. Qualifying standards for 2027 have not been published either, regardless of specific times circulating on aggregator sites. The race's page on 42cal is worth checking again closer to when that window is expected to open.
The only hill comes at mile 26
After 25-plus miles with nothing steeper than an overpass, the course saves its one real climb for the very end: a bridge on Roosevelt Road, about 25 feet of rise, that finishers and course guides alike have nicknamed Mount Roosevelt. Coach's panel of finishers described it as feeling like a mountain, more of an overpass than a bridge, arriving right after the long straight run down Michigan Avenue, at the point in the race where a runner has the least left to give. A short downhill follows, then the finish, back in the same Grant Park where the loop began. Twenty-five feet of climb is a small thing on paper. After 26 miles on a course this balanced, it is still the last thing standing between a runner and the line.
