If you need to stop and walk for 5 minutes in the middle and then restart the run, it's an option.

I tell myself that I can do it, but when it comes down to it my stupid machismo type-A personality rears its head and I "gut" through it. Which sucks, as I've injured myself a couple times and had the whole internal conversation that goes like...

"I should stop..."
"Scr3w that, suck it up and RUN girly man..."

I swear I can hear my old high school soccer coach yelling at me from my subconscious...

When are you planning on running your marathon?

It's been years -- like 36 -- since I did long-distance running. I'm sure the "science" has changed a lot. I would agree with a previous poster that pacing is hugely important. Slow and steady wins the race, as the old saying goes. At least with respect to the first half of the run. What is your goal? To complete? Or do you have a time you want to achieve? If it's a time, then make sure it's a reasonable amount of time. I would advise anyone, though, to plan merely to complete their first marathon.

Are you changing your route on a regular basis? I found this very helpful. The "been here done this" feeling can get in your way sometimes.

I personally always found the 10 mile moment to be pretty amazing. I'd run the first five very slowly, and then increase my speed only slightly for the second five. My body would seem to invite me to increase speed somewhere around nine or 10 miles.

I also found it helpful not to run "miles" per se but from place to place. Since I was always running in San Francisco's Golden Gate Park it was very easy to find landmarks to run from and to and to plan my training around those distances rather than "miles." Of course, the park was magical for that since I lived at the end of it furthest from the ocean and could always have the ocean be one of the places I ran to. Also, if your other half is up for it, have him meet you at the eleven or twelve-mile moment to cheer you on.

But I think the most important thing is not to overdo. If you're running 15 miles for your long run, you should be running about 45 miles during the week. I think most people work up to this too quickly. I personally think that in addition to having days you don't run that you should have weeks with greatly reduced running times. It's important to remember that 15 miles is a long distance. Just like nine. Just like three. Also, make sure you've got a food program that's supporting long-distance running! The long run every week requires as much food planning as the actual marathon.

You've got this.

How many miles are you running per week?

I would tend to agree with the slowing down. I have run 9 halves and 1 full marathon. I would run almost all of my runs at about the same pace which wasn't more than 40 seconds slower than my half PR...I would finish the runs, but they were hard and they sucked and i began to not really like running. I stalled on any progress on my half time, so I hit the trails...I have signed up for a 50K trail race this fall. I just ran 20 miles last weekend on the trails averaging 11 minute miles (2 minutes slower than my half pace) and it felt great, almost easy. Last year training for my full I was running no slower than 10:30's but more closer to 9;45's...and i faltered hard at my full...I had pushed myself too hard the entire training cycle. I have fallen back in love with running (mainly running the trails) by simply slowing down.

Ditto on slowing down. Nearly every training program I've looked at emphasizes the longest runs of the week are supposed to be about endurance and not speed.

To the OP - because I know you do slow down on your long runs (though arguably not enough) I'd also add that the shortest runs of the week are not about speed either - they're about recovery. If I'm running less than 5 miles (unless it's a tempo session with a LONG warm-up) it's a recovery run and it's going to be slower than any of my other running.

I don't think I need to slow down any of my runs. My 5K PR is 22', my 1/2 marathon PR is 1:56'. And my marathon goal is 4:30. Using the calculator you provided, it would seem I'm right on target.

I still think you do - based on your 5k PR the training paces sound okay, but if you just put your half marathon PR into the calculator (or based on your marathon goal), the suggested training paces are a lot slower. As you're struggling at longer distances, I'd really recommend following those. For perspective, when you go out and do your short and medium runs, you are running close to or faster than half marathon PR pace. That's really hard work, and something my coach wouldn't let me do without a 3-mile warm-up and half-mile cool-down either side. The effect of this is you can't complete your long runs because you've tired yourself out during the week.

You're also trying to do your long runs faster than your target marathon pace, which never ends well.

This is right on the money. Couldn't have stated it better myself.

Same thing happened to me during my first marathon training. Only advice I have is to suck it up and keep on going. When I ran the Atlanta marathon my brother met me around mile 20 and ran a few with me. Totally picked my spirits up. Wish he could do it again for me in October. Keep up the training and eat right. The mental part is all you.