What pace should the long run be? What about the tempo? And how do I know what I’m capable of over a marathon when I’ve never run one?

The answer’s been sat in your Saturday morning all along.

Years back I was stood in the boyfriend position outside a shop in York, flicking round on my Fenix, and it threw up a set of race predictions. The 5k was a second off the course record at Barnsley parkrun. The marathon was a twelve and a half minute PB. Is that really what I can do right now? In a basic world with no variables, maybe. In the real one, with hills and wind and the small matter of actually getting round, not a chance.

Watch predictions are optimistic. A recent parkrun isn’t. Proper effort, course you know, people dragging you round. Most useful number you’ve got.

Get an honest 5k first

Only works if you raced it. One where you jogged round chatting tells you nothing. You want the last six to eight weeks, and you want to have finished properly cooked.

Hilly course? Knock a few seconds off in your head. Not all parkruns are equal and anyone saying otherwise hasn’t run Barnsley.

Turning 5k into everything else

Rough conversions from a well-run 5k. Rough is the right word.

• 10k — 4 to 5 per cent slower per mile
• Half marathon — 8 to 9 per cent slower
• Marathon — 15 to 17 per cent slower

A 20:00 parkrun is 6:26 a mile. That points at 6:44 for 10k, 7:00 for a half, 7:26 for a marathon. A 3:15 marathon on paper.

On paper. The marathon one is the least reliable by a distance, because it assumes you’ve done the endurance work to hold it. A 20 minute parkrunner off 25 miles a week is not running 3:15, whatever the maths says.

The training paces, which is what you wanted

Same 20:00 parkrun.

• Easy — 8:00 to 8:45 a mile. Yes, that slow
• Steady — around 7:30
• Marathon pace — around 7:26
• Threshold — around 6:50. Comfortably hard, an hour-race effort
• Intervals — around 6:20. Roughly your parkrun pace

Two minutes a mile between easy and intervals. If your easy days and session days are within thirty seconds of each other you’ve collapsed the lot into one grey middle speed. That’s where progress goes to die.

Redo it every couple of months

Paces built off a parkrun from last February aren’t your paces. Race one properly every six to eight weeks and rebuild off the new number.

It’s free. It’s five kilometres. There’s one near you on Saturday.

Do it your way. Just do it off real numbers, not what the watch reckons.

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My personalised training plans do all this for you. Every session at your own paces, off your own recent time, with the reasoning behind each one. £39, lands as a PDF.