Pacing is the cheapest time you will ever find. Two runners with the same fitness can finish minutes apart, just because one went out too fast. This guide covers how to choose a goal pace you can actually hold, how to spread your effort over each distance, and what to do on the day when things do not go to plan.
Even, negative and positive splits
A split is the time for one part of the race, usually each kilometre or mile, or each half.
- Even splits: every part at about the same pace.
- Negative splits: the second half faster than the first.
- Positive splits: the second half slower than the first.
Most distance world records have been run with even or slightly negative splits. The fastest way to cover a distance is to spread your effort evenly, with whatever you have left used at the end.
Most ordinary runners do the opposite. They run positive splits, fast early and slowing later, and it is rarely a choice. It just happens because the start feels so easy.
Why going out too fast costs the most
Going out too fast is the most common pacing mistake in the half and the marathon. In the first few kilometres you are rested, excited and surrounded by people, so goal pace feels easy, and a bit quicker feels fine too.
The problem is that running even a little above the pace you can sustain burns through your energy faster than it feels like it does. You do not pay straight away. You pay later, when you slow down far more than the seconds you gained at the start. Banking time early almost never works. In longer races, it is much easier to lose a minute in the last few kilometres than to gain one in the first few.
Choosing a realistic goal pace
Your goal pace should come from what you have actually run, not what you hope to run.
- Start from a recent race. A race or time trial from the last couple of months is the best guide to your current fitness. Any distance works.
- Convert it. Put that time into the race time predictor or the VDOT calculator to see what it suggests for your race distance.
- Be honest about your training. Predictions assume you have trained properly for the distance. A marathon prediction from a 5K is often optimistic for newer runners who have not done the long runs.
- Adjust for the day. Heat, humidity, wind and hills all slow you down. On a hot day, start slower than planned and adjust by feel.
As a rough example from Run-R's VDOT engine: a 25:00 5K runner is predicted about 51:53 for a 10K, 1:55:04 for a half and 3:57:55 for a marathon. A sensible half marathon goal for that runner might be around 1:55 to 2:00. The marathon figure is the one to treat with most caution.
The training paces page explains how VDOT works if you want the detail.
How to pace each distance
| Race | First part | Middle | Where to push |
|---|---|---|---|
| 5K | First km at goal pace, not faster | Hold on, it hurts from halfway | Last km |
| 10K | First 2 to 3 km at or just under goal pace | Settle and hold | From 7 to 8 km |
| Half | First 5 km at or a touch slower than goal | Hold steady to 15 to 16 km | Last 5 km |
| Marathon | First half should feel easy | Hold steady to 30 km | From 30 to 35 km, if you can |
5K
The 5K is short enough that it hurts from early on, so the job is not to make it hurt too soon. Many people run their first kilometre far too fast. Aim for goal pace and accept it may feel slightly too easy. Kilometres two to four are where races are won or lost; hold your pace when it starts to bite. Push in the last kilometre. The 5K pace chart gives the splits for any target time.
10K
Run the first couple of kilometres controlled. The middle section is about concentration: keep the pace honest when it starts to feel hard. If you are still on pace at 7 or 8 km, start to press. See the 10K pace chart.
Half marathon
The first 5 km should feel easy, almost too easy. Hold goal pace through the middle, and treat the last 5 km as the race. If you have something left, use it from there. The half marathon pace chart has the splits.
Marathon
The marathon punishes early mistakes more than any other distance. The first half should feel comfortable, and you should be able to talk in short sentences. The real race starts somewhere after 30 km. If you get there feeling in control, you can pick up. If not, holding pace is a win. The marathon pace chart covers goal times from fast to steady.
Pace bands, splits and your watch
A pace band is a strip on your wrist with the target time at each kilometre or mile marker. It takes the maths out of race day. You can print one with your splits from the pace band page.
Here is something that catches people out. Your GPS watch will often show more distance than the course, so by the end it says you have run further than the official distance. That is partly GPS error and partly because courses are measured along the shortest possible line, which you will not run exactly. If you pace off the watch's live pace, you can end up slower than you think.
So use the course markers. Check your time at each kilometre or mile marker against your pace band. That is the number that counts. Use the watch's live pace as a rough guide, not the final word.
Race-day food and drink
Eat breakfast 2 to 3 hours before the start. Keep it familiar: something you have eaten before long runs, mostly carbohydrate, not too much fibre or fat. Toast, porridge, a bagel or a banana are common choices. Sip water in the hours before, then stop drinking a little before the start.
During the race:
- 5K and 10K: little or nothing needed. Water if it is hot.
- Half marathon: many runners manage on water alone, but if you will be out for more than about an hour, a gel or two can help.
- Marathon: aim for 30 to 60 g of carbohydrate per hour, the long-standing guidance. Up to about 90 g an hour is possible for events over about 2.5 hours, using glucose and fructose mixes, but only if you have trained your gut to take it. Most gels are about 20 to 30 g, so check the label. Start early rather than waiting until you feel empty.
Drink to thirst. Forcing down extra water is not safer: over-drinking can cause hyponatraemia, which is dangerous. Practise your race-day fuel on long runs first. The long run guide covers how.
Mental tactics
Long races are easier to manage in pieces. Split the race into chunks and only think about the one you are in. For a half, three blocks of about 5 km and a final push. For a marathon, the next mile marker or the next drinks station.
Use short cue words when it gets hard. Keep them simple and about what to do: "relax", "smooth", "tall", "quick feet". Telling yourself what to do works better than telling yourself what not to do. Practise them in hard training sessions so they are ready on the day.
Expect a bad patch. Many races have one. It often passes if you keep going, take some fuel and relax your shoulders.
When it goes wrong
If you feel chest pain, dizziness or faint, stop and get help from race medical staff. No time is worth it.
Otherwise:
- You went out too fast. Ease back now, not later. Losing a few seconds per km straight away costs far less than blowing up.
- It is hot. Slow down from the start, drink to thirst and pour water over yourself. Adjust your target.
- You are falling off pace. Change the goal. Hold a pace you can manage and finish well. A slower time run well is better than a crash.
- A stitch or cramp. Slow down, breathe out fully, and walk for a short while if you need to.
It is fine to walk a drinks station, too. A few steps of walking to drink properly costs very little time.
Train for the pace you want to race
Run-R builds a plan from a recent race time, with goal pace work in the peak weeks of half and marathon plans so it feels familiar on the day. Build one from the plan builder, and when race week comes, read the taper guide too.