How to Set a Realistic Half Marathon Goal Time

Setting a goal time for a half marathon is harder than it looks. Set it too ambitious and you go out too fast, blow up at kilometer 14, and limp home frustrated. Set it too conservative and you cruise to the finish knowing you had more in you. Neither is satisfying.

Most runners set their goal one of three ways: they copy a friend's time, they pick a round number that sounds good ("I want to break 2 hours"), or they use a race predictor and trust it completely. Each of these approaches ignores the most relevant information available: your actual current training data.

Here's a more honest method.

The problem with race predictors

Race time calculators take a recent result — say, a 10K time — and extrapolate to longer distances using standard aerobic degradation curves. Garmin's Race Predictor does this. Running calculators like those on Runner's World do this.

They work reasonably well for runners with very consistent training. For everyone else, they introduce predictable errors:

They assume consistent training volume. A 10K PR set during a period of high volume will overpredict your half marathon capacity if you've since reduced training.

They don't account for heat, elevation, or course profile. A flat spring 10K and a hilly autumn half marathon are not directly comparable.

They can't see your current fitness. Your most recent 10K might be six months old. Your aerobic fitness changes significantly over that time, in either direction.

They assume your aerobic base matches the distance. Good half marathon performance requires a developed aerobic base. Runners who excel at 10K on raw speed often underperform at the half without adequate base mileage.

A better approach: using your training pace data

Your training paces reveal more about your race-ready fitness than any single race result. Here's how to extract a realistic goal:

Step 1: Find your current threshold pace.

Your lactate threshold pace is roughly the pace you can sustain for 60 minutes of all-out effort. A good proxy: the pace of your tempo runs, or a recent hard effort on a flat course.

If you've been doing structured tempo work, your threshold pace is the effort where breathing is controlled but definitely labored — you can speak in short phrases, not full sentences.

Step 2: Apply the threshold-to-race conversion.

Half marathon race pace typically falls at 90–95% of your threshold pace for trained runners, and slightly higher (closer to threshold) for less experienced runners.

Practically: if your current threshold pace is 5:00/km, your realistic half marathon target is 5:15–5:30/km, depending on your aerobic base and race conditions.

Step 3: Adjust for your fitness trend.

Is your threshold pace improving? Has your easy run heart rate been dropping at the same speeds? These are signs your aerobic fitness is developing. If you're six weeks out from your race and improving, you can aim slightly more aggressively.

If your training has been disrupted — illness, travel, life stress — aim at the conservative end.

How to read your Garmin data for race prediction

Your Garmin provides several metrics useful for goal-setting:

VO2max estimate: Garmin's VO2max predictor is imperfect but consistent. A rough correlation for half marathons: VO2max 45 → ~2:10 HM, VO2max 50 → ~1:55 HM, VO2max 55 → ~1:43 HM, VO2max 60 → ~1:32 HM. These are population estimates — use them as a sanity check, not a precise target.

Lactate threshold pace: Garmin estimates this from tempo-effort activities. If the estimate feels too slow, you may not have had enough clean threshold data in your recent training history.

Training load trend: If your training load (TRIMP) has been consistently above your chronic baseline for the past 4–6 weeks, your fitness is developing. If it's been below, you may be underestimating the recovery debt in your fitness estimate.

Setting your A, B, and C goals

One of the most useful race planning frameworks is the three-goal approach.

C goal (minimum success): Finishing healthy and feeling in control in the second half. A time 5–7% slower than your realistic target. You hit this even on a bad day.

B goal (realistic target): Your honest, data-informed target based on current training. You hit this on a good day with solid execution.

A goal (dream scenario): Your B goal minus 2–3%. You hit this if everything goes right — good weather, good sleep, great pacing, feeling strong. Pursue this if you're on track at kilometer 10.

Having three goals removes the all-or-nothing mentality and gives you a framework for real-time decision-making during the race.

Pacing strategy: the thing that ruins most races

Once you have a realistic goal time, the pacing strategy is simple and most runners still get it wrong: run the first 10km slightly slower than goal pace, run the last 11km at or slightly above goal pace.

The anatomy of a half marathon blow-up is almost always the same: aggressive first 7km, controlled middle, then the wheels come off at kilometer 15. The runners who set PRs almost universally run even splits or slightly negative splits (second half faster than first).

The temptation at the start is enormous — you feel fresh, the crowd energy is high, your goal pace feels easy. Treat that as a trap. Your aerobic system hasn't had time to warm up fully, your glycogen is untouched, and your effort feels deceptively light. Hold back.

The honest conversation about goal-setting

The most useful thing you can do is be honest with yourself about your current fitness — not your fitness three months ago, not your fitness after a perfect 12-week block, but your fitness today.

The runners who race well consistently are the ones who set goals based on current evidence, not aspiration. They're not pessimistic — they leave room for the A goal. But they don't gamble their entire race on hitting a time that requires things to go perfectly.

Use your data. Set a B goal that represents honest current fitness. Race the first half conservatively. Let the second half tell you what you've built.

That's the framework. Your training data has the answer — you just need to listen to it.