Try Out the Marathon Pace Calculator...

Three Essential Running Calculators That Help You Conquer Your Marathon

Going out too fast is the single biggest reason marathons fall apart in the second half. These three marathon pace calculators exist to stop that happening to you. You'll find a race conversion calculator to estimate your marathon time from a recent race, a training pace calculator to build your easy, tempo and long-run paces around a goal time, and a marathon pace chart built for negative splits.

I want to be straight with you about what these calculators are and what they aren't. They predict what's possible with the right endurance behind it — they don't guarantee anything, and they don't replace the long runs. Treat the output as a target to build towards, not a pace you're entitled to on race day.

The three calculators are:

Race Conversion Calculator - Use a recent race performance to estimate your marathon time. Use this one first — it's your best guard against going out too fast.

Marathon Training Pace Calculator - Enter your goal marathon time and get the training paces that align to it — easy pace, tempo pace, interval pace and reps. You can also run this in reverse: enter your current training paces and work back to a likely marathon time.

Marathon Pace Chart - Based on your goal marathon time, this gives you a full split chart. The thing is, this chart assumes negative splits — so it looks a little different from the standard charts you'll find elsewhere. Read the notes below it. They matter.

Every calculator comes with its own set of explanations.

My advice to you: read the guidance that comes with each calculator. Each one has a specific use and real limitations — understanding both will get you a much more sensible result.


Running Calculator #1: Race Conversion Calculator

Race Conversion Calculator
The race I ran had a length of	MilesKilometres
Use dots, no commas. So 26.2 miles, not 26,2...
My time was (hh:mm:ss)	: :
Press the button, don't click Enter
Predicted time for your next marathon (hh:mm:ss) :

The Small Print of the Race Conversion Calculator

Keep these three points in mind when you use this calculator.

Longer races are better predictors - For marathon prediction, the race you use as a predictor needs to be long enough. 5k is too short. 10k is so-so. 15k is getting there. A half marathon and above is really useful. Don't rely on shorter races alone — a short race almost always gives you an overly optimistic marathon time prediction.

Use a recent performance - Pick a recent race performance. Don't rely on a personal best from a year ago to set your marathon goal time. Your current fitness is what counts — not where you were twelve months back.

Back it up with the right running training - This is the most important point on this page. Endurance is key in the marathon. Many of us — I'd say 90–95% of us — falter in the last part of the race. Usually because we haven't done enough 20-milers and runs over 90 minutes.

Interested in doing the race conversion for any type of race, not just the marathon? Then simply go to the Race Conversion Calculator page.



Running Calculator #2: Marathon Training Pace Calculator

Marathon Running Training Pace Calculator
What is the goal marathon time?		: : (hh:mm:ss)
Press the button, don't click Enter
Corresponding marathon running training paces
Easy Pace :		/ mile	/ km
Tempo Pace :		/ mile	/ km
Interval Pace :		/ km	/ 400 m
Fast Reps :		/ 200 m	/ 400 m

Small Print of the Marathon Training Pace Calculator

This calculator has more moving parts than the first one — and I'd urge you to use it with care.

You can use it in two ways.


1. Use a marathon goal time to calculate corresponding running training paces.

Suppose you'd like to run your marathon in a certain time. Enter that goal time and the calculator gives you the corresponding training paces — easy pace, tempo pace, intervals and reps.

If those paces are genuinely close to where your training is right now, your goal time is within reach.

Here's the critical point: forcing yourself to run much faster in training is a certain road to injury. These training paces need to come to you naturally — through progressive, consistent training.

Example. Suppose you'd like to run a 3:59 marathon.
This provides you with:
Easy pace of 6:20 min/k (10:12 min/mi)
Tempo running pace of 5:17 min/k (8:31 min/mi)
Interval pace of 1:57 / 400m (4:53 min/km)
Reps pace of 1:46/400m (53sec/200m)

Suppose your current easy pace is 6:30 min/km, not 6:20 min/km. You're not far off. My advice is to leave it there — don't artificially push yourself to run 6:20 min/km. Through diligent training your easy pace will get faster over time. Only when your natural easy pace reaches 6:20 min/km does 3:59 become a sensible goal.

And here's something I want to be clear about: it's not just your easy pace that needs to line up. Your tempo pace AND interval pace need to be right as well.


2. Work out your likely marathon time based on your current running training paces.

The second way to use this calculator is to work back from your current training paces to a realistic marathon time.

When you train regularly, you probably have a clear sense of your easy pace, tempo pace and interval pace.

With a bit of trial and error, you can find the marathon time that matches those paces.

Example. Suppose your easy pace is 5:30 min/km and your marathon is three weeks away. What's a realistic target time?

Try a few different times and see what rolls out.

Enter 3:40 (3 hrs and 40 min). The easy pace that comes back is 5:52 min/km.

Enter 3hr30. The easy pace becomes 5:36 min/km.

Enter 3hr20. The easy pace becomes 5:21 min/km.

Enter 3hr25. Easy pace is then 5:29 min/km.

Enter 3hr26. The easy pace is exactly 5:30 min/km.

You can quite quickly close in on the marathon time that corresponds to your current training pace.


Make sure that all your running training paces point to the same performance level. Your easy runs may suggest you can run a 3 hr 26 min marathon. But your tempo runs may indicate a 3 hr 50 min marathon. In that situation, always rely on the slower outcome, not the faster one.


Running Calculator #3: Marathon Pace Calculator / Marathon Pace Chart

Marathon Running Pace Chart (Negative Splits)
What is the goal marathon time?		: : (hh:mm:ss)
Press the button, don't click Enter
Time for First Half:		Pace: / mile	/ km
Time for Second Half:		Pace: / mile	/ km
Mile Splits		KM Splits
4 Miles		7 km
8 Miles		14 km
12 Miles		21 km
Half Way Mark		Half Way Mark
16 Miles		28 km
20 Miles		35 km
24 Miles		42 km
Finish Time		Finish Time

Small Print of the Marathon Pace Chart Calculator

a) This marathon pace chart assumes negative splits

b) This marathon pace chart does not provide splits for every mile/km

More and more people are catching on to the idea that running with negative splits (first part of the race slower than the second part) is a good idea for the marathon.

There are many benefits to running your marathon this way.

It protects you from starting off too aggressively. Especially if you happen to have a bad day. It provides a massive boost in confidence and a lot of motivation to be hunting down runners and to be passing dozens and dozens and dozens in the second half. And it mimics how many world records have been set.

To the second point, the reason I am not providing splits for every km / mile is that most races are not exactly flat or allow for exact even splits for every mile / km.

I think it makes more sense to split it up in the way I have done.

Hope these calculators have been useful to you.

Once you have your goal pace, PlanMyRace builds a personalised marathon plan around your race date, current fitness and available training days, with paces set from a recent race result and a proper taper.

Some Other Pages You May Like

What Time to Expect in the Marathon Is 3:30 a Realistic Goal for My First Marathon? Sub-4:20 Marathon Goal – How Do I Get There? Training Paces to Aim for in Marathon Training 18 Months to a Marathon – Is It Doable? Marathon Fueling Strategy Easy Run Pace for Non-Speed Runs Strength Training for Runners

Home > Running Races > Marathon Training Tips > Marathon Pacing Plan > Marathon Pace Calculator

  ☕ Buy Dom a Coffee