Your First Marathon — a Sub-4:00, 18-Week Plan

The 10K was about VO2max. The half was about threshold and holding a pace twice as long. The marathon is about none of that. 42.195 km. Sub-4:00 means 5:40/km — a pace slower than your easy long-run friends would call a jog.

And that's the trap. 5:40/km is easy. For the first 30 km it will feel like you could hold it forever. Then, somewhere past 32 km, your body runs out of stored carbohydrate, your legs forget how to lift, and the last 10 km become a different sport entirely. The marathon isn't 42 km. It's a 32 km warm-up and a 10 km survival test. This plan is built around that second number.

This plan assumes you can already run a half marathon in about 1:55–2:05, or a 10K under 52 minutes. If not, build the base first with sub-90 half or sub-50 10K.

What sub-4:00 pace feels like#

• Full conversation is possible — you could talk in paragraphs, not just sentences
• Breathing: relaxed, roughly 3 in, 3 out
• Heart rate: 75–80% of max (lower than a half — this is the discipline)
• The pace should feel almost too slow for the first half. That's correct. The marathon punishes anyone who feels good early.

The number itself is not hard. Holding it after three and a half hours on your feet is the entire challenge. You're not training your speed. You're training your body to keep producing 5:40/km when its fuel tank is empty.

Three differences between the half and the full#

	Half (sub-90–2:00)	Full (sub-4:00)
Deciding factor	threshold + endurance	fat metabolism + glycogen + durability
Longest long run	24–28 km	30–34 km
In-race fueling	1 gel	4–6 gels + electrolytes
The real test	last 5 km	km 32 to 42 — "the wall"

The half ends before your fuel runs out. The marathon does not. Past roughly 32 km your glycogen stores empty, and if you haven't trained your body to burn fat and haven't eaten enough on the road, you hit the wall — the pace drops 60–90 seconds per km and no amount of willpower brings it back. Everything in this plan exists to push that wall past the finish line.

The 18-week plan#

Five blocks. Weeks 4, 8, 12, and 16 are cutback weeks. The plan peaks at week 15, then a three-week taper.

Wk	Mon	Tue	Wed	Thu	Fri	Sat	Sun
1	Rest	8K Easy + strides	10K Easy	6K Tempo @5:15	Rest	18K Long	6K Recovery
2	Rest	8K Easy + strides	10K Easy	8K Tempo @5:15	6K Easy	20K Long	6K Recovery
3	Rest	10K Easy + strides	12K Easy	5×1km @5:00	6K Easy	22K Long	6K Recovery
4	Rest	8K Easy	8K Easy	8K Tempo @5:15	Rest	16K Long	Cutback wk
5	Rest	10K Easy + strides	12K Easy	10K Tempo @5:10	6K Easy	24K Long	7K Recovery
6	Rest	10K Easy	13K Easy	4×2km @5:00 (90s jog)	6K Easy	26K Long	7K Recovery
7	Rest	11K Easy + strides	13K Easy	12K Tempo @5:10	7K Easy	28K Long (last 6km @5:40)	7K Recovery
8	Rest	8K Easy	10K Easy	6×1km @4:55	Rest	18K Long	Cutback wk
9	Rest	10K Easy + strides	14K Easy	3×3km @5:05 (2 min jog)	8K Easy	30K Long (last 8km @5:40)	7K Recovery
10	Rest	11K Easy	14K Easy	14K Tempo @5:10	8K Easy	26K Long	8K Recovery
11	Rest	11K Easy + strides	14K Easy	2×5km @5:05 (3 min jog)	8K Easy	32K Long (last 10km @5:40)	8K Recovery
12	Rest	8K Easy	10K Easy	8K Tempo @5:10	Rest	20K Long	Cutback wk
13	Rest	11K Easy + strides	14K Easy	16K Tempo @5:10	8K Easy	30K Long (last 12km @5:40)	8K Recovery
14	Rest	11K Easy	14K Easy	4×3km @5:00 (2 min jog)	7K Easy	34K Long (last 8km @5:40)	8K Recovery
15	Rest	10K Easy + strides	12K Easy	12K Tempo @5:10	6K Easy	28K Long (last 10km @5:40)	7K Recovery
16	Rest	8K Easy	10K Easy	8K @5:40 (race pace)	Rest	20K Long	Taper begins
17	Rest	8K Easy + strides	8K Easy	10K @5:40 (race pace)	5K Easy	14K Long	6K Recovery
18	6K Easy	Rest	6K Easy + strides	5K @5:40	Rest	Marathon	Recovery

Five to six runs a week, peaking around 70–85 km. Bracket Tempo and Interval sessions with 1.5–2 km warm-up and cool-down (table distances are the main set). Total volume matters less than the long runs — do not skip a single one.

Four core workouts#

1. The long run — the whole plan in one session#

Longest 32–34 km @6:20–6:50, with race-pace blocks at the end

This is the marathon. Everything else is support. The long run trains the three things that decide your race: fat metabolism, glycogen storage, and the durability to keep your form past three hours. Run them slow — a full minute slower than race pace — except for the marked race-pace finishes.

2. Race-pace finishes — rehearsing the wall#

The last 6 → 8 → 10 → 12 km of long runs at 5:40

This is the marathon-specific weapon. Anyone can run 5:40 fresh. The skill is running it on tired, glycogen-depleted legs — exactly the state you'll be in at km 32. Every race-pace block at the end of a long run is a dress rehearsal for the only part of the race that's hard.

3. Tempo / Threshold — the aerobic ceiling#

10–16 km @5:10 (30 sec faster than goal)

The marathon isn't a threshold race, but a higher threshold makes 5:40 feel easier and pushes back the point where you start burning glycogen. The 16K tempo in week 13 is the toughest session in the plan — if you finish it, the marathon's pace will feel gentle.

4. Intervals — keeping a little top end#

5–6×1km @4:55

Just enough speed work to stop 5:40 from ever feeling fast. One short, faster-than-goal session a week keeps your economy sharp without the injury risk of heavy intervals. The marathon is built on volume, not speed — these are seasoning, not the meal.

Fueling — the race you win in the kitchen#

A trained body stores roughly 90 minutes of glycogen at marathon pace. The race takes four hours. The math is the whole problem. You cannot store enough — you have to eat on the road.

• Start early, eat often. First gel at 45 minutes (~8 km), then one every 30–40 minutes. Five to six total. Don't wait until you feel empty — by then it's too late.
• Carbs: aim for 60–90 g/hour. That's roughly 2–3 gels per hour for the back half. Modern dual-source (glucose + fructose) gels let you absorb more.
• Electrolytes on hot days. A marathon in Bangkok heat is a sodium race as much as a carb race. Salt tablets or electrolyte drink, especially past 25 km.
• Drink to thirst, at every station, while holding pace. Small sips. Don't stop, don't gulp.
• Carb-load the two days before — 8–10 g/kg/day. This is the one race long enough to justify it.

Recovery — when long runs pass three hours#

Past the 30 km mark, recovery is more than half of training. A 32 km long run can take 4–5 days to fully absorb.

• Sleep 8+ hours — guard it ferociously the two nights after a long run
• Protein 1.6–2.0 g/kg/day
• Carbs 6–8 g/kg/day, climbing before long runs
• Within 30 min of a long run: carbs + protein (the glycogen window)
• Easy days truly easy — 6:30/km or slower. The temptation to push easy runs is what ends marathon training blocks.
• Foam roll and stretch daily during peak weeks

Injury warning signs#

Marathon volume breaks people who ignore these. Any one of them and you take a full week down:

1. Inner-knee pain on stairs (runner's knee)
2. Achilles soreness on the first morning step
3. Heel pain in the morning (plantar fasciitis)
4. Front-shin tightness or swelling (shin splints)
5. Resting HR up 5+ BPM for three straight days (overtraining)

At 80 km a week, fatigue accumulates faster than you think. One down week beats six weeks off with a stress fracture.

Race-day strategy#

A sub-4:00 marathon is a flat even pace or the slightest negative split. The penalty for going out fast is the cruelest in all of running — the wall does not negotiate.

Segment	Pace	Note
0–10 km	5:42	Hold back hard. It will feel insultingly easy. Good. First gel at 8 km.
10–25 km	5:40	Settle into goal. Gel every 30–40 min. Drink every station.
25–32 km	5:40	The pace gets honest now. Stay relaxed, keep eating. This is where discipline pays.
32–42 km	5:40 → empty it	The wall. If you fueled and paced right, you hold. The last 2 km, everything left.

Run the first 10 km at 5:25 and you will pay for every second after km 32 — with interest. The most common first-marathon failure isn't a lack of fitness. It's a fast, joyful, fatal opening 15 km. Trust the plan: boredom in the first half is the price of strength in the second.

• Two days out: 6K Easy + 4 strides. Otherwise rest and carbs.
• Day before: full rest, finish carb-loading, lay out your kit, no alcohol, nothing new on your feet.
• Race morning: familiar breakfast 3 hours out, ~600–800 kcal of carbs. Caffeine if you normally take it. Leave time for the bathroom — twice.
• Warm-up: barely any. 1 km jog and a few strides. You have four hours to warm up on the course; save everything.

Sub-4:00 done. Now what?#

You're a marathoner. That sentence doesn't expire.

Next:

• Sub-3:30 marathon (4:58/km) — the next great wall, where speed work returns in force
• Sub-90 half (4:15/km) — turn back toward speed; see here
• A second marathon — the one where you finally believe the first wasn't luck

The 10K asks how fast you are. The half asks how long you can hold it. The marathon asks a quieter question: when the fuel is gone and the legs are done, who are you?

If eighteen weeks felt long, it's because the marathon is long. Distance is the most honest race there is — it gives back exactly what you put in, and not one kilometer more.