How accurate is the McMillan pace calculator for you?

Frightening accurate at all distances for me. Within a few seconds every time.

Bill

I've used it as my bible since I started and it's generally accepted that their marathon time is very aggressive - by 10 mins seems a common range. You need to do high mileage and good quality to nail that time (but it's possible if you have a good day!). Every other time I'm also within seconds. 

So 3:58 for you would be a pretty certain goal, with 3:48 if you're doing great. But I wouldn't get greedy and think 3:45 is going to be a snap. 

I would say that for marathon especially, McMillan has in mind 60-70mpw minimum and very focussed.

In particular, how do you run your long runs?  On 60-70mpw, training for a marathon, I'd suggest that you need to be running them pretty hard.

I follow the Pfitz 18/70 plan, so there's usually a handful of goal marathon pace long runs (like, 18 with the last 14 at GMP). Aside from that, most of my long runs (18+) are between 9:20-9:30, which is maybe 30 seconds off my goal marathon pace.

Well, that sounds pretty good.  Sorry, I got nothin else...

For medium and medium-long distance it is ok, for short distances it is way off.  For marathon I think it is 5-10 min fast and maybe the assumption is that you are putting in marathon mileage.  My half marathon to 10k is accurate, but it is a minute too slow on my mile.  

Calculator is sort of all over the place in my opinion 

I find the calculator to be quite accurate for races from 5k to HM. I haven't done a marathon recently, though I suspect that its prediction for my fall marathon is a little optimistic, even if I put in the mileage that I want to do.

We shouldn't necessarily blame the calculator for being bad at predicting marathon times. One thing that it can't do is know what distances are our forte. And probably few of us are of the type that simply gets better as the race gets longer. In my case I know that McMillan is slightly pessimistic over 5k and shorter distances. And this fits with the fact that my background is as a 800-1500 runner on the track. 

Please don't take this post the wrong way -- I'm just throwing this observation out there as something to think about.  If it were getting me right for 10K - HM but off by a full minute for the mile, I'd be pretty concerned that I wasn't hitting my potential in those longer races.  I haven't run an open marathon in a few years, but the calculator has been quite accurate for me from HM down to the mile, so maybe I'm just biased by this fact....

Based on my last 10k in December, the McMillan calculator spit out a number that I thought was ridiculously fast for a half marathon.  I trained pretty well for the HM, which took place 3/31 (built up to >40mpw).  I actually surprised myself and went within 11 seconds of the McMillan time.

What are your times for your last few HMs if any? (I don't think I've hit 100km in a week yet, ugh, props to you for your consistency)

i've gotten within a minute or so of my McMillan prediction for 2 marathons.  The predictions were based on a half mary just 2 months prior in each case.  

that said- it took pushing myself until my eyes bled to do it.

double post

I have no idea where you're seeing skipped workouts -- I've done every one on the 18/70 plan, without fail. I ran a marathon on March 17, so you may be seeing the taper for and recovery from that. I also ran a 10-mile race on April 1. I'm now building again for a marathon on May 6. 

I've been running for probably 10 years, ran my first marathon in 2009, have run six marathons. I've used the Pfitz 18/55 plan twice and am on my third time with the 18/70 plan.

Current marathon PR is a 4:04, which I ran during the March marathon. Ran it VERY conservatively on a unseasonably hot day.

Do you not think that with ideal temps and aggressively appropriate pacing you would be a lot closer to the predicted 3:48?

The difficulty with hitting the pace predictors for a Full Marathon has a lot to do with the difficulty in running the perfect race.  There are so many variables to a Full.  Weather, pacing, nutrition and hrdration, dodging and weaving, etc.  And it can be tricky to pace that fine line between too slow, right on, and too fast.  Only a few seconds per mile one way or the other, can make or break that all-important last 10K, where the Marathon really starts.

Training properly and consistently can sometimes be an issue as well.

Bill

Possibly...maybe someday all of the factors will align! My May marathon is Flying Pig in Cincinnati, which sounds like a challenging course...so I'd be over the moon with sub-4.