Half Marathon Pace Calculator

Use the Half Marathon Pace Calculator

Convert goal finish time to per‑km and per‑mile pace or set a target pace to see expected splits for 21.1 km.

How to Use Half Marathon Pace Calculator

1. Step 1: Choose Input Mode

   Pick “Finish Time → Pace” or “Target Pace → Time” for 21.1 km.

2. Step 2: Enter Time or Pace

   Type your goal finish time or target pace using mobile‑friendly fields.

3. Step 3: Select Pace Unit

   If using Target Pace mode, pick /km or /mi to match your training.

4. Step 4: Add Options

   Optionally include warm‑up, cool‑down, gel interval, and elevation notes.

5. Step 5: Calculate & Review

   Tap Calculate to see per‑km and per‑mile paces, key splits, and a fueling plan.

Key Features

• Key 5K/10K/15K/20K splits
• Per‑mile split table (13.1)
• Finish Time ↔ Pace modes
• Warm‑up and cool‑down add‑ons
• Gel reminders and course notes
• Print‑friendly plan

Understanding Results

Formula

Distance, time, and pace are directly related: pace = time ÷ distance and time = distance × pace. For a fixed half marathon distance of 21.0975 km (≈13.1094 miles), the calculator divides your finish time by 21.0975 to get pace per kilometer and by 13.1094 to get pace per mile. Average speed follows from pace: km/h = 3600 ÷ seconds per km, mph = 3600 ÷ seconds per mile.

Key splits are reported at 5K, 10K, 15K, 20K, and the finish to make pacing checkpoints easy to remember. A separate per‑mile table shows cumulative times through Mile 13 and the final 0.1 mile.

Reference Ranges & Interpretation

Half marathon finish times vary widely. Many recreational runners finish between about 1:30–2:30, while advanced runners may target 1:10–1:25 and elites much faster. The best strategy for most athletes is even to slightly negative splits—start controlled, hold your target rhythm through the middle, and finish strong in the last kilometers.

Use the per‑km and per‑mile pace together with course knowledge. On a net‑uphill route, let early splits run a few seconds slower; on a net‑downhill course, avoid excessive early surges that can cause late fatigue.

Assumptions & Limitations

Calculations assume an accurately measured course, steady conditions, and consistent effort. Real‑world results depend on terrain, temperature, wind, altitude, crowding, and how you execute fueling and pacing. Treat the numbers as planning guidance, not medical advice. Practice race pace in training and adjust on the day for conditions.

Complete Guide: Half Marathon Pace Calculator

Plan your 21.1 km race with the half marathon pace calculator: convert goal time to precise per‑km and per‑mile pace, plus 5K/10K splits and finish time.

How to read your pace table

Use the 5K, 10K, 15K, 20K, and finish checkpoints as anchors. If you are ±5–10 seconds off per‑km early, resist surges; let the middle third settle the rhythm.

Numbers are only useful when they become decisions. This guide turns your pace and split table into a simple race plan you can use from the first kilometer to the finish. We keep the language plain and the steps practical so you can focus on running, not on math.

At a glance: pacing anchors

• First 5 km: keep it calm—no faster than target pace.
• Middle 10 km: settle into rhythm; check splits every 3–5 km.
• Final 6 km: squeeze gradually if you have it; avoid big surges.

Build a simple 21.1 km race plan

Think in thirds: controlled start, steady middle, honest finish. Use the per‑km and per‑mile splits from the half marathon pace calculator to spot early surges and to time gels and aid‑station checks.

Why pace matters in a half marathon

The half marathon rewards patience. Many runners start too fast, spike their effort in the early kilometers, and pay for it at 15–18 km. A steady pace protects your legs and breathing while keeping you on track to meet your time. Your target pace acts as a governor in the first third and an anchor through the middle. When the final 3–4 km arrive, you can squeeze the pace without tipping into an early fade.

If you mostly train by pace, keep your units consistent—per‑kilometer or per‑mile—so your brain has less to translate on race day. If you train by heart rate for your easy runs, you can still use pace to set the ceiling at the start and guide your steady effort later. Tools like our running pace calculator make it easy to convert between speed, pace, and time in everyday training.

How to set a realistic goal time

Pick a goal grounded in what you have done recently—not what you hope to do. If you have a fresh 10K or 5K result, use that to triangulate. The simplest method is to examine your average pace in those races and ask if you can reasonably hold a slightly slower pace for 21.1 km. For a data‑driven approach, you can estimate fitness using our VDOT calculator or VO2 max calculator, then map those results back to training paces and half marathon predictions.

Your weekly long run, tempo runs around lactate threshold, and aerobic base mileage tell you just as much as pure speed. If your longest recent run is 12–14 km, your first thought shouldn’t be an aggressive PR. Use your next few weeks to nudge your long run toward 18–22 km, keep one threshold workout, and run easy enough on the other days to recover well.

When you choose a goal, run a dress‑rehearsal workout two to three weeks before race day. Example: 3 × 5 km at projected half marathon pace with 3–4 minutes easy jog between reps. If the final rep requires straining, your target might be a little ambitious; if you finish strong, confidence is warranted. Keep the day civilized—avoid turning it into an all‑out race so you arrive fresh to the start line.

Another option is a threshold‑based session such as 8–10 km continuous at a comfortably hard effort that you could hold for roughly an hour. If this pace sits noticeably faster than your planned half pace, you’re likely in a good spot. If it drifts slower or breaks into many micro‑surges, consider nudging your half goal a few seconds per kilometer to the conservative side.

How to use the half marathon pace calculator effectively

Open the tool and choose your input style. If you already know your desired finish time, select “Finish Time → Pace” and enter hours, minutes, and seconds. The calculator outputs per‑km and per‑mile pace, average speed, and detailed splits. If you prefer to target a pace, select “Target Pace → Time”, enter minutes and seconds per kilometer (or per mile), and the calculator will project your finish time for 21.1 km.

Add optional warm‑up and cool‑down distance to estimate the full session. You can also set a gel interval—many runners use every 35–45 minutes—and jot quick elevation notes to remind yourself where to stay conservative. When you tap Calculate, you get key 5K/10K/15K/20K splits and a per‑mile table. Review them for reasonableness and adjust your target if the plan looks unrealistic.

If heart rate helps you regulate effort, you can cross‑check your plan with our target heart rate calculator or dial in easy‑day recovery using the zone 2 heart rate calculator. On hot or windy days, consider a few seconds per kilometer adjustment and prioritize steady effort over rigid numbers.

Even vs. negative splits for 21.1 km

Even splits—holding the same pace for the full distance—work well for most runners. Slight negative splits, where the second half is a touch faster than the first, are also reliable. A practical strategy is to start the first 2–3 km a few seconds slower than target pace, settle to target by 5–6 km, and hold it through 18 km. If you have the legs, squeeze 3–5 seconds per kilometer over the last 3 km and close hard in the final 800 meters. Positive splits, where you start fast and slow later, are common but usually reflect early optimism rather than good planning.

Adapt on the day

Let conditions set small guardrails. Heat, wind, and hills change how a given pace feels, so protect effort first and allow the split to float a few seconds when needed. Use your split table as the anchor and decide one kilometer at a time.

Build the course profile into your plan. On net‑uphill courses, begin more conservatively. On net‑downhill routes, avoid getting greedy too soon or the eccentric muscle load can make the last 5 km feel longer than they are. If the race is crowded, pre‑plan how you will navigate the first kilometer so you don’t surge wildly around groups and spike your effort.

If you wear a GPS watch, lock the lap button to manual splits or auto‑lap at 1 km or 1 mile. Use the split beep as a gentle metronome: assess, adjust one click if needed, and return your eyes to the road. Staring at live pace makes many runners tense; cumulative split time is calmer and more informative. If your watch allows multiple fields, pair lap pace, total time, and heart rate so you can judge effort at a glance.

When the course has notable hills, anchor your plan to effort. On climbs, keep your breathing controlled and your stride compact; don’t try to “protect” the exact split at all costs. On descents, float into slightly quicker steps without pounding. Over 21.1 km, this even‑effort approach typically yields better overall time and a stronger final section.

Fueling and hydration basics

Most runners benefit from a small carbohydrate intake during a half marathon, especially when the race lasts longer than about 75–90 minutes. A common pattern is one gel 10–15 minutes before the start and then a gel every 35–45 minutes during the race, adjusted for your stomach and experience. Practice in training so nothing is new on race day. If you start with a full gel, you might take one around 8–10 km and another at 16–17 km for a two‑gel plan.

Hydration is personal. Conditions, sweat rate, and pace all matter. Take small sips of water or a sports drink at aid stations, aiming for comfort rather than a specific volume. On hot days, drink earlier and a bit more often; on cool days you may need very little. For your everyday routine, our water intake calculator can help you estimate a baseline daily target outside of racing.

Remember: more is not always better. Over‑drinking can lead to stomach slosh and, in rare cases, hyponatremia. Small, regular sips paired with your fuel plan are usually sufficient. If you find yourself skipping every other station because the table is crowded, that’s fine—keep your effort smooth and return to your pace promptly.

If you are sensitive to caffeine, check your gel labels. Some products contain moderate caffeine, which can help alertness for certain runners, but it may also irritate the stomach. Trial different options well before race week. If your race offers on‑course nutrition, try a packet in training so you know how your body responds.

Practice fueling during long runs

Use a few long runs to rehearse your gel timing and sip pattern at goal pace. Note what sits well, how your stomach feels in the last third, and which stations on your course map line up with your plan. Good practice turns fueling into a calm habit on race day.

Finally, fuel logistics are part of pacing. When you know a gel is coming up, consider taking it just before a flat section or right as you approach a station so you can drink a sip afterward. Avoid fueling on steep climbs or while weaving through crowded turns. These small details reduce stress and help you maintain steady rhythm.

Training ingredients that drive results

The simple recipe includes: a weekly long run, 1–2 workouts anchored around threshold or steady efforts, and plenty of easy miles to absorb the work. Threshold runs (20–40 minutes near comfortably hard) teach you to hold a steady pace without red‑lining. Long runs of 18–22 km develop durability so your legs still respond late in the race. Many runners like a mid‑week steady run around marathon pace to link endurance and rhythm—our marathon pace calculator is a handy reference for that session.

Speed work has a role, but it should support rather than dominate your week. Short intervals sharpen mechanics and leg turnover, while longer repeats (e.g., 1–3 km at threshold) build strength specific to half marathon pace. Use strides (20–30 seconds fast with full recovery) after easy runs to keep your stride lively without adding stress.

If you want a simple 8‑week outline: start with three base weeks (easy running + strides + one short threshold segment), then three build weeks (longer long run, longer threshold blocks, and an occasional marathon‑pace segment), one sharpening week (reduced volume, some faster but short pickups), and a race week taper. Keep easy days truly easy—your body adapts during recovery, not in the red.

Strength training twice per week (20–30 minutes) pays dividends: focus on single‑leg stability, calves, hamstrings, and glutes. Two sets of 6–10 controlled reps go far. Stronger legs resist late‑race breakdown, which often shows up as fading cadence and heavy footstrike, costing seconds you otherwise earned with good pacing.

Adjusting for terrain, weather, and race logistics

Your plan should bend with the day. Headwinds make the effort feel harder at the same pace, while tailwinds can silently lift your speed. Heat and humidity slow almost everyone; altitude also matters. If the forecast is warm, start conservatively and use the early stations. On a hilly course, focus on effort: allow a few seconds per kilometer to drift on climbs and get them back gradually on the descents without bombing the downhill.

Logistics matter too. Locate the corrals, restrooms, and bag drop the day before if possible. Know which side of the road the early aid stations are on. If GPS reception is noisy downtown, use your split table as the truth and treat the live pace on your watch as a clue rather than a command.

If you travel across time zones, adjust your sleep a few days early and keep pre‑race meals familiar. On cold mornings, wear a throwaway layer you can drop at the start and consider thin gloves for the first kilometers so your hands stay relaxed. If rain is likely, a light cap can keep water out of your eyes and make the day feel calmer.

Shoes and socks should be unremarkable: comfortable, tested, and free of surprises. If you race in plated shoes, include a few key workouts in them so your calves are accustomed to the geometry. Race morning is not the time to experiment with a new insert or a different lacing style.

Race‑day execution checklist

A short list you can mentally rehearse:

• Breakfast 2–3 hours before, plus a small top‑off 30–60 minutes before if you tolerate it.
• Warm‑up 10–20 minutes easy, a few form drills, and 2–3 short strides.
• First 2–3 km: hold back a touch; let the field settle.
• Middle 10–12 km: lock into rhythm; take scheduled gels and small sips.
• Last 3–4 km: squeeze if you have the legs; run the tangents.
• Final 800 m: pick a landmark, stay tall, and drive to the line.

If you train on a treadmill, translate your target pace to speed using km/h or mph and incline 1% to approximate outdoor cost. You can also sanity‑check treadmill paces with the 5K pace calculator to see how your shorter efforts align with your half goal.

Finally, keep your self‑talk simple. A short cue like “tall and smooth” or “hold rhythm” beats complicated calculations mid‑race. Glance at your split, make one small adjustment, and move on. The calmest runners often run the most even races.

How to read and learn from your splits

After the race, compare your actual splits to the plan. If the first 5K was significantly faster than target, that likely explains mid‑race fade. If your splits were smooth and you still slowed late, durability may be the next lever: slightly longer long runs, a few more steady kilometers, or more patient early pacing. If your watch distance exceeds 21.1 km, don’t be discouraged—courses measured on the road can run long on watches when tangents are not followed, and GPS drift adds a little noise.

Write two short notes within 24 hours: what worked and what you’d change next time. That small habit pays off. Then plug your next target into this tool and sketch the following month of training with realistic rhythm. Race plans improve quickly when you close the loop between intention and outcome.

If you intend to step up in distance, translate today’s performance to marathon training paces with the marathon pace calculator. If you plan to sharpen for a shorter race, use your new fitness to estimate targets with the running pace calculator and keep one threshold session in the week so your stamina holds while speed improves.

Recovery and next steps

Give yourself time to absorb the race. The first few days are for easy movement and sleep. By the second week, you can reintroduce short strides and light aerobic work. If your next stop is the marathon, build volume patiently and use marathon‑pace work sparingly at first. If you’re chasing 5K or 10K speed, sharpen with controlled intervals and keep a weekly threshold session to maintain strength.

Whenever you set a new goal, return to this calculator to translate that goal into actionable paces and splits you can trust. Keep your plan simple, review your key splits, and run the race in front of you.

Frequently Asked Questions