Quick Answer
A 3:45 marathon requires an average pace of 5:20 per km (8:34 per mile). Half way: ~1:52:30. Key benchmark: a half marathon PB of 1:43–1:48. Training volume: 50–70 km/week over 12–16 weeks. Strategy: aim for a slight negative split — first half in 1:53:00, second half in 1:52:00.
3:45 Marathon Pace: The Numbers
To finish a marathon in 3 hours 45 minutes, you need to average 5:20 per kilometre or 8:34 per mile. Here’s what that looks like at every major checkpoint:
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| Distance | Target Split (even pace) |
|---|---|
| 5 km | 26:40 |
| 10 km | 53:20 |
| 15 km | 1:20:00 |
| 20 km | 1:46:40 |
| Half (21.1 km) | 1:52:30 |
| 25 km | 2:13:20 |
| 30 km | 2:40:00 |
| 35 km | 3:06:40 |
| 40 km | 3:33:20 |
| 42.195 km (Finish) | 3:45:00 |
In practice, running perfectly even splits is rare. A smarter approach is a slight negative split: pass halfway in about 1:53:00–1:54:00 (a few seconds per km slower than target), then gradually lift the pace in the second half. This conserves glycogen early and lets you finish strong rather than fading after 30 km.
Use a running pace calculator to dial in your exact target splits if you’re aiming for 3:44 or 3:46 rather than dead-on 3:45.
Are You Ready? Benchmark Times
Before committing to a 3:45 marathon goal, check your shorter-distance times. These benchmarks suggest you have the aerobic capacity to hold 5:20/km for 42 km — with proper marathon-specific training:
| Distance | Benchmark Time | What It Tells You |
|---|---|---|
| 5 km | 22:00–23:30 | Strong speed base. You can run well below marathon pace. |
| 10 km | 46:00–49:00 | Good aerobic fitness. You can sustain a hard effort for ~50 min. |
| Half marathon | 1:43–1:48 | The best predictor. If you're in this range, 3:45 is realistic. |
| Previous marathon | 3:50–4:05 | You've done the distance. Now the focus is pacing and efficiency. |
If your half marathon PB is slower than 1:50, a 3:45 full marathon may be a stretch. Focus on building your aerobic base and improving your stamina before targeting this time. A race time predictor can help you estimate a realistic marathon goal from your current fitness.
Training Structure for a 3:45 Marathon
Most runners targeting 3:45 need 50–70 km per week during peak training, spread over 4–5 runs. The training block should last 12–16 weeks, building progressively with a 2–3 week taper before race day. Here’s what a typical peak week looks like:
Sample Peak Training Week (~60 km)
| Day | Session | Details |
|---|---|---|
| Monday | Rest or cross-train | Recovery day. Walk, yoga, or easy cycling. |
| Tuesday | Intervals | 5 × 1 km at 4:50–5:00/km with 90 sec jog recovery. Builds speed and running economy. |
| Wednesday | Easy run | 8–10 km at 6:00–6:30/km. Truly easy — heart rate zone 2. |
| Thursday | Tempo run | 4 km warm-up, then 6–8 km at 5:05–5:15/km (marathon pace +/- 10 sec), 2 km cool-down. |
| Friday | Rest or easy 5 km | Keep it light. Legs need to absorb the week's work. |
| Saturday | Easy run | 8 km at 6:00–6:30/km. |
| Sunday | Long run | 28–32 km. First 20 km easy (5:50–6:10/km), last 8–12 km at or near marathon pace (5:15–5:25/km). |
The long run is the centrepiece. Build it gradually: start at 20–22 km and add 2–3 km per week until you reach 30–34 km. Include at least two long runs with the final 8–12 km at marathon pace — this teaches your body to hold 5:20/km on tired legs, which is exactly what race day demands.
If you’re newer to structured training, a beginner marathon training plan can provide the week-by-week progression you need. Once you’ve built your base, the sessions above will sharpen your fitness for a specific time goal.
The Three Key Workouts
1. Tempo Runs (Marathon Pace Control)
Run 6–10 km at 5:05–5:20/km — right around your goal marathon pace or slightly faster. This teaches your body to clear lactate at the pace you’ll hold for 42 km. A good tempo run should feel controlled but firm — not a flat-out effort. You should be able to speak a few words, but not hold a conversation.
2. Interval Sessions (Speed and Economy)
Intervals at faster-than-marathon pace improve your running economy and make 5:20/km feel more sustainable. Try 5–6 × 1 km at 4:45–5:00/km, or 8 × 800 m at 4:30–4:45/km, with 60–90 seconds recovery. These sessions build the speed reserve that prevents you from running right at your limit on race day. Interval training principles apply directly to marathon prep — the paces just shift.
3. Marathon-Pace Long Runs (Race Simulation)
Your most important sessions. Run 28–32 km total, with the last 10–12 km at 5:15–5:25/km. This simulates the fatigue you’ll feel after 30 km on race day and builds the confidence that you can hold pace when it matters. Include your planned race-day fuelling strategy (gels, hydration timing) to test everything in training.
Race-Day Strategy: How to Pace a 3:45 Marathon
The single biggest mistake in marathon racing is starting too fast. Even 10–15 seconds per km too fast in the first 10 km can cost you minutes in the final 10 km. Here’s a segment-by-segment plan:
Kilometres 1–10: Settle In
Target: 5:25–5:30/km. This will feel easy — that’s the point. Resist the adrenaline. The crowds will push you to run faster. Don’t. You’re banking energy for later. If your race has a 3:45 pace group, run with them or just behind them.
Kilometres 10–21: Find Your Rhythm
Target: 5:20/km. Settle into your goal pace. Check in with your breathing — it should be controlled, not laboured. Start fuelling: first gel at about 45–60 minutes, then every 30–40 minutes. Drink at aid stations — small sips, don’t skip them.
Kilometres 21–30: Hold Steady
Target: 5:18–5:20/km. This is where the race begins. Your legs will start to feel the distance. Focus on form: upright posture, relaxed shoulders, consistent cadence. Keep fuelling. If you’re on pace at 30 km, you’re in a strong position.
Kilometres 30–42.2: Dig In
Target: 5:15–5:20/km. The last 12 km is where marathons are won or lost. If you paced correctly, you should have enough left to hold or slightly increase pace. Break it into smaller chunks mentally — “just get to 35 km” then “just 5 km to go.” Focus on one km at a time. The finish will come.
Fuelling for a 3:45 Marathon
At 3:45, you’re running long enough to fully deplete glycogen stores. Without proper fuelling, you will hit the wall — typically around 28–32 km. Here’s the plan:
Before the race: Eat a carb-rich meal 2–3 hours before the start. Something familiar that sits well — toast with jam, porridge with banana, or a potato-based meal the night before to top up glycogen.
During the race: Start fuelling at 45–60 minutes (before you feel like you need it). Take a gel or energy chews every 30–40 minutes. Aim for 30–60 grams of carbohydrates per hour. Wash gels down with water, not sports drink — combining them can cause stomach distress.
Hydration: Drink at every aid station — small sips of water or electrolyte drink. Don’t wait until you feel thirsty. In warm conditions, electrolytes become even more important.
Critical rule: Never try a new gel, drink, or food on race day. Test everything during your long training runs first.
How 3:45 Compares to Other Marathon Goals
| Goal Time | Pace/km | Pace/mile | Typical Weekly Volume | Half Marathon Benchmark |
|---|---|---|---|---|
| Sub 4:00 | 5:41 | 9:09 | 40–55 km | 1:52–1:58 |
| Sub 3:45 | 5:20 | 8:34 | 50–70 km | 1:43–1:48 |
| Sub 3:30 | 4:59 | 8:01 | 60–85 km | 1:37–1:42 |
| Sub 3:00 | 4:16 | 6:52 | 80–110 km | 1:25–1:28 |
If 3:45 feels ambitious from where you are now, work on building the aerobic base and volume first. If you’re already running half marathons faster than 1:43, you may be ready to aim for sub-3:00 or sub-3:30 with the right preparation.
Common Mistakes That Derail a 3:45 Attempt
Starting too fast. Going out at 5:10/km because it feels easy will catch up with you by 30 km. Trust the pace. The first 10 km should feel almost boring.
Skipping fuelling. Your body can store about 90 minutes of glycogen at marathon pace. After that, you need external fuel. Skipping gels because you “feel fine” at 15 km guarantees a wall at 32 km.
Not enough long runs. You need at least 3–4 runs of 28 km or longer in training, with the longest at 30–34 km. Without these, you won’t have the muscular endurance for the final 12 km.
All runs at the same pace. If every run is at 5:30–5:40/km, you’re running too fast on easy days and too slow on hard days. Polarise your training: easy days at 6:00–6:30/km, hard days at or below marathon pace.
Ignoring the taper. Reduce volume by 30–40% in the final 2–3 weeks. Keep some intensity (short tempo efforts, strides) but drop the overall volume. You should arrive at the start line feeling rested, not fatigued.
FAQ: Running a 3:45 Marathon
What pace do I need for a 3:45 marathon?
5:20 per km (8:34 per mile). Pass halfway at about 1:52:30 on even splits, or 1:53:00 if planning a negative split.
What half marathon time predicts a 3:45 marathon?
A half marathon PB of 1:43–1:48 suggests you have the aerobic fitness. If you’re slower than 1:50, build your base first.
How many km per week do I need?
50–70 km per week during peak training, over 4–5 runs. Consistency over 12–16 weeks matters more than any single big week.
Should I run even splits or negative splits?
Negative splits are recommended. Run the first half in ~1:53:00 and aim to lift slightly in the second half. This avoids early glycogen depletion.
How should I fuel during the race?
First gel at 45–60 minutes, then every 30–40 minutes. Aim for 30–60 g of carbs per hour. Test everything in training first.
Your Path to 3:45: Where to Start
A 3:45 marathon is achievable for most runners who are willing to train consistently for 12–16 weeks at 50–70 km per week. The key ingredients: a half marathon PB in the 1:43–1:48 range, weekly long runs that build to 30+ km, regular tempo and interval sessions, and a disciplined race-day pacing plan. Nail the preparation, trust the pace on race day, and the time will come.
Our marathon coaching programmes build your fitness progressively with paced long runs, structured speed work, and race-day strategy — all tailored to your schedule and your goal.
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