Half Marathon Pacing Strategy: Hold Back Early, Own the Last 5K
At 5K in a half, “comfortable” is a trap. Opening 8–15 sec/km fast feels smooth because glycogen and adrenaline are full — then 15–18K becomes survival. The conflict is not motivation versus laziness; it is early surplus versus a finish you can still accelerate into.
Set the Goal From Evidence, Not Hope
Use a recent 10K or long tempo, then the Race Predictor, before you pick a finish time. Build even-split baselines with the Pace Calculator and Pace Chart. If the predictor says 1:47 and you want 1:42, race 1:47 with a stretch option late — do not open at 1:42 pace.
Worked Scenario: 1:45 Half (4:58/km)
- First 3K: 5:02–5:06/km (restrained open)
- 5K: 25:00–25:15
- 10K: 49:45–50:15
- 15K: 1:14:30–1:15:00
- 16–21.1K: hold 4:56–5:00, then push only if 10K and 15K were clean
Forty-five seconds ahead at 10K is usually a loan against the last 5K. Ease to goal pace for 2–3K, take fluids as practiced, and reassess at 15K.
HR, Hills, and Fuel
Pace leads; HR confirms. Expect ~5–10 bpm drift at constant pace after ~30 minutes — set context with the HR Zones Calculator. On hills, hold effort and trust cumulative checkpoints. Practice gels/fluids in long runs; late-race decisions assume early fueling already happened. Hot days: shift toward RPE and splits, not cool-weather HR targets. More race-morning detail: race-day nutrition.
Predictors do not know your fueling, heat, or hills. A clean 10K time trial predicts half fitness better than an all-out 5K. Wrist HR on rolling courses is noisy; if pace holds and RPE is stable while HR creeps, prefer pace. If pace falls while HR climbs, you are in trouble regardless of the readiness score on your watch.
Final-5K Decision Rule
Push the last 5K only if 10K and 15K checkpoints were inside the plan and form is intact. If you are already outside the window or fading, lock cadence and protect form — finish the race you are in, not the fantasy split. Race morning: write the four checkpoint times on your hand or bib and obey them through 15K. If weather is hotter than training, shift the whole plan 5–15 sec/km slower before the gun — do not discover heat mid-race and still chase the cool-weather number.