Your Goal Pace for Chicago: The Detailed Numbers and the App That Saves You From the Most Common Mistake

The Mistake That Costs an Entire Marathon

Every September I get the same message: "Henri, my marathon PR is 3:45 — is that my goal for Chicago?" And every time, I have to ask the same uncomfortable question: when did you run that 3:45?

The answer is almost always "a year ago" or "in my last marathon, before the injury / the baby / six months without real training." That number, however real it was at the time, no longer describes the person who's going to stand on the start line in Grant Park. It describes a different version of that runner.

This is, by a wide margin, the most expensive pacing mistake I see in my work with PMPRunning athletes. It's not nutrition, it's not shoes, it's not even Chicago's weather (which can be generous or brutal — more on that below). It's heading out at a pace that matches a fitness level you no longer have, or don't have yet.

Why Last Year's PR Doesn't Apply

Physiology changes fast, in both directions. The training volume accumulated over the last 8–12 weeks — not the last 12 months — is what determines your current aerobic capacity, your running economy, and your lactate tolerance on race day. Biomarkers of exercise stress and adaptation reflect relatively short time windows: mitochondrial remodeling, capillary density, and shifts in substrate utilization respond to recent stimulus, not to whatever stimulus you were under a year ago [PMID:41922043].

Put another way: your body doesn't "remember" the marathon you ran 12 months ago in a way that transfers directly to race day. There may be some residual base — a bit of muscle memory, some more durable cardiovascular adaptation — but the specific pace you held that day was the product of a specific training block that no longer exists in your current body.

I've seen this mistake go both ways:

• The nostalgic optimist: uses their old PR, goes out aggressive, and collapses at kilometer 30 because their current fitness can't hold that pace.
• The injury-cautious pessimist: got hurt 8 months ago, has since recovered and trained well this cycle, but is still anchored to fear and runs too conservatively, leaving minutes on the table.

Both are making the same underlying error: using an old data point instead of a recent, relevant one.

The Right Way: Derive Your Pace From a Recent Race

The most reliable way to project your marathon pace is to use a recent benchmark race — ideally a 10K or half marathon run in the last 4–8 weeks, under similar conditions (weather, terrain, genuine effort level).

Equivalence formulas — like the ones popularized by Peter Riegel and refined over decades of race data — work reasonably well for intermediate distances, but they lose accuracy as the distance jump grows. Projecting a marathon from a recent 5K is less reliable than projecting from a recent half marathon, simply because the metabolic endurance and glycogen-management component of the marathon isn't well represented in a race that short.

My hierarchy of confidence, from most to least reliable:

1. Half marathon run in the last 6–8 weeks — the best available reference.
2. Recent 10K + current training volume (weekly mileage, longest long run, time spent in threshold zone).
3. Recent 5K — useful, but requires a conservative adjustment, especially for athletes with a thin endurance base.
4. Threshold pace measured in training (a controlled tempo run, for example) — very useful as a cross-check.

Never rely on a single number. Cross-reference at least two data sources before committing to a goal pace.

Approximate Equivalence Table

This table uses the Riegel formula with a marathon-specific fatigue adjustment (the final 12–15 km of a marathon impose a metabolic cost that pure extrapolation doesn't fully capture, which is why the derived marathon pace is slightly more conservative than a raw mathematical projection).

Recent 10K	Recent Half Marathon	Estimated Marathon Pace	Estimated Finish Time
40:00	1:28:00	6:43 min/mile	2:56:00
43:00	1:35:00	7:14 min/mile	3:09:30
46:00	1:42:00	7:44 min/mile	3:22:30
50:00	1:50:00	8:19 min/mile	3:38:00
55:00	2:01:00	9:07 min/mile	3:59:00
1:00:00	2:12:00	9:57 min/mile	4:20:00
1:07:00	2:28:00	11:06 min/mile	4:50:00

These numbers are starting points, not verdicts. Adjust based on your prior marathon experience, your known heat tolerance, and how your benchmark race actually felt (was it a true max effort, or did you run with something left in the tank?).

Chicago's Specific Terrain and Why It Matters for Your Pacing

The Chicago course is fast — nearly flat, winding through 29 neighborhoods with very few meaningful elevation changes, according to the course profile published by the marathon itself. That's a real advantage for holding an even pace, but it brings two technical considerations that a lot of runners overlook.

GPS signal loss through the urban course. The route passes through stretches with tall buildings, particularly in the Loop and parts of downtown, where your watch's satellite signal can bounce between skyscrapers (the "urban canyon" effect). This produces erratic instantaneous pace readings — sometimes flashing absurdly fast or slow paces for a few seconds — even when your actual effort is perfectly steady.

My practical recommendation, the same one I give every athlete before big urban marathons:

• Don't trust instantaneous pace through skyscraper stretches. Use average lap pace or perceived effort as your primary reference in those segments.
• Set your watch to display averaged pace (lap pace or a rolling average over the last 400–800m) instead of raw instantaneous pace.
• Memorize the official mile/kilometer markers on the course and use the physical race markers as your reality check when the GPS starts acting up.
• Don't make sharp pace adjustments off a single anomalous watch reading. Wait to confirm the trend over at least 300–400 meters.

This detail sounds minor until you watch a runner suddenly surge because their watch showed a fake "slow" pace, burning glycogen reserves they'll need at kilometer 35.

Why Physiological Margin Also Matters

It's worth remembering that the marathon, especially for runners over 40, imposes a real and measurable cardiovascular load. Recent research on the cardiac effects of prolonged endurance exercise shows that both young and older athletes experience acute changes in cardiac function after long efforts, and that recovery of these markers takes time [PMID:40667749]. This reinforces the idea that your goal pace shouldn't be the theoretical maximum your physiology "could" hold on a perfect day — it should be a pace with reasonable margin that respects the accumulated cost of the last several hours of effort.

As a masters runner myself (I compete in the 3000m in the 45-49 age group), this isn't abstract theory for me: the margin between "ambitious pace" and "reckless pace" narrows with age, and respecting that margin is what lets you keep competing year after year.

How I Use the PMPRunning Calculator With My Athletes

To avoid doing these calculations by hand every time — and to avoid the bias of picking the number we "like best" instead of the number the data actually supports — I built a pace calculator that I use in planning sessions with my PMPRunning athletes.

The tool takes your recent benchmark (10K, half, or both) and your current training volume, and returns:

• Goal marathon pace adjusted for race-specific fatigue.
• A pace range broken down by course segment (first 10K, middle stretch, final 10K).
• Reference paces for your key workouts (tempo, threshold, intervals) derived from the same base data point, so your whole plan is calibrated off one consistent number instead of a mix of different formulas.

You can download it for free at pmprunning.com/pmpruncal. I especially recommend it in the last 6–8 weeks before the race, once you have a fresh, real benchmark from this training cycle.

Practical Recommendations for the Weeks Ahead

1. Get a real benchmark race in the next 2–3 weeks if you don't already have one: a genuine-effort 10K or half marathon, not a workout disguised as a race.
2. Discard any benchmark older than 10–12 weeks as the basis for your goal pace. Use it only as historical context.
3. Cross-reference at least two data sources (recent benchmark + threshold pace from training) before locking in your final number.
4. Practice running by effort, not just by watch, on your long runs in the coming weeks — especially on stretches where you simulate running "blind" without constantly checking the GPS.
5. Break your pacing plan into course segments instead of a single flat pace: Chicago's first 10K calls for restraint, the middle stretch calls for patience, and the final 10K is where the race is actually decided.
6. Use the calculator to keep your goal pace consistent with the training paces you've been hitting these past few weeks.

Final Thought

The correct goal pace isn't the one you'd most like to run, and it isn't the one you ran on your best day a year ago. It's the one your current data, interpreted honestly, tells you that you can hold for 26.2 miles. That number exists, it's calculable, and it doesn't require guessing. It only requires looking at the right data and respecting what it says, even when your ego would prefer a different number.

---

References

• Siebers M, Bizjak DA. Exercise biomarkers. Adv Clin Chem. 2026. [PMID:41922043]
• Frandsen J, Aaroe M, et al. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]
• Couvert A, Goumy L, et al. Effects of a Cycling versus Running HIIT Program on Fat Mass Loss and Gut Microbiota Composition in Men with Overweight/Obesity. Med Sci Sports Exerc. 2024. [PMID:38233990]
• Szuhany KL, Bugatti M, Otto MW. A meta-analytic review of the effects of exercise on brain-derived neurotrophic factor. J Psychiatr Res. 2015. [PMID:25455510]
• Chicago Marathon. Course & Participant Information. chicagomarathon.com/event-info/participant-information/course/