A few things indicated to me that I would BQ: 1) My HM times were consistently pointing to an equivalent BQ time (I am suspicious of 5k times as good indicators). 2) Long runs were not a daunting thing to me. So I would say that for ME, it was good weekly speedwork, regular decent LRs and about 50 mile weeks.

High weekly mileage helps, of course, but it does not have to be 70-80 miles per week (at least not for me). Solid 50 mile weeks with good speedwork were enough at the time. But of course, I was like 100 years old when I had my first BQ, so I didn't need a 3:40. :-) I run faster BQs these days, but it's probably due to the accumulated mileage on my legs and the few years of experience. I still don't run very high mileage, but my HM time is faster now. I try to maintain my regular mileage, but I work on getting faster instead.

EDIT: I misread, you need sub-3:40? Gulp... unless you're some miracle of nature, like our running mama here, I would try to do my best in my first, but not be disappointed if the BQ does not happen. 3:40 for a first, for a woman, isn't that easy!

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Particularly with lower mileage runners, and for a marathon 35 mpw is low, calculators are overly optimistic.  A more realistic time based on current fitness would be 4:10-4:15. Bumping up your mileage will help but you should also maintain some quality runs, even intervals. Having picked a May marathon, you may have added an additional barrier to surmount in a BQ attempt. Depending on which marathon you selected, you may run into warm or even hot temps, which will slow you down. Hills and altitude will also. Plan your training to deal with the potential conditions you may face on race day.

Thanks! That is what I thought but sometimes you get to dreaming big and you need others to reign you in to reality!

Do I think I can BQ on my first try? Not really. I haven't given a fInish time much thought actually since until recently, it was to finish running and that was it

My mileage does steadily increase until April, with a 2 week high of 54mpw before taper begins. In reality, I'd like that as a base mpw long term before I feel ready to try for bigger & better things. But obviously, that won't stop me from trying to do the best my training allows this May. Even if it isn't even a sub 4 hour finish!

Thanks everybody!

It's not just the lower training mileage that makes 5Ks less accurate as predictors, it's also the difference in energy demands on the aerobic and anaerobic energy sources. Probably the best correlation I've gotten between a 5K and the marathon was a 17:44 5K which predicts a 2:52:48 and my 2:56:36. That's still a 4 minute differential, though that wasn't a particularly good marathon race for me - started way too slow, sped up too much, then hit the wall. I was also running 65 mpw and even topped 300 miles one month.

Lol! I enter my current pace time for a 10 miler(last 2 training runs at 1:27) and it gives me a marathon finish of 4:04! 

I do get that stamina and endurance have a lot to do with factors in a 26.2 mile race and a 5k really isn't endurance based at all.  I just got greedy when I punched in the numbers. I would think my 5k being 2 months from current training would mean I would do a better 5k now but if I ran a marathon NOW there would be no way I would finish in 4:04! I haven't ran a half distance LR all at once yet! So I get that a calculator is just a guess really, based on a number that might have no correlation with RL.

Thanks for talking me down off the ledge, BFers!

 A 5K is highly endurance based. It's not at all unusual to see top 5K runners logging 80-90 mpw. But the difference between what percentage is endurance based rises quite a bit from 5K to 10K, hence 10K is about the shortest distance that would give a halfway reliable indication of a marathon time.

You probably know my story, but I BQd with a 3:32 in October, 7 months after I started running.  It's definitely possible!  Your 5K is a crummy predictor of your marathon time anyway, so I wouldn't worry about that.  Do you have any other longer race times?  10K or HM are best.  I'd go out and race one or do a time trial and see what you've got.

All I did to get my time was run a lot of miles and follow a plan.  I averaged 74 mpw throughout training.  I'd add as many miles as you can.  It doesn't have to be 70, but as many as you can handle.  You are probably running those 10 milers too fast unless you are a heck of a lot faster then me. You can take a look at my log and see how I'm running my runs as far as paces go.  The good thing is that you are such a new runner, like me, that you are going to get faster pretty quickly.  That rules!  My original projected MP early in training was 8:40 and a later TT projected 7:53 pace.  I ran 8:07 pace in the race, but I really think I could've run 7:57-8:00 had I paced smarter.  Here's my RR with more info.

http://forums.runnersworld.com/forums/runner-communities/beginners/rr-des-moines-marathon-went-couch-bq-7-months-after-started-running-pics?plckFindPostKey=Cat:Runner%2520CommunitiesForum:608106477Discussion:88f46dd8-dbc7-4c43-bc6d-9160849007e7Post:89ae2238-cc58-4c3b-91a6-d6217ebbbbb3

Anyway, let me know if you have any questions, but my main advice would be to run more miles, slow down those runs and pick a solid training plan. 

Unfortunately, you can run a lot of miles per week and still be ill-prepared to BQ.

I've run two marathons so far, and the training was glaringly different:

race 1 using Higdon Int. 2 --  Mileage was usually between 55-65, long runs were done at roughly goal MP plus1:00.  There would be one tempo run per week of about 10 miles at MP minus :15ish.  Long easy runs, lots of easy filler miles, and a weekly half-assed speed day did not yield a BQ.  They yielded a perfectly good 13.1, increasing feelings of "hmm, are we there yet?", and then a spectacular meltdown to walking and pained jogging from 18 miles onward.

race 2 using Pfitz 18/70 -- Mileage was usually 60+, peaking over 70.  Most long runs were improved to goal MP plus :30 or less.  There were no fluff days, everything served a purpose.  Recovery days followed intense ones, and only rarely did recovery pace dip much below MP plus 1:00.MLR's involved chunks of tempo or VO2 max stuff, LR's sometimes contained large servings of miles run sub-MP, and then there was the one workout that erased any doubt about being able to BQ.  2 weeks before the race, 17 miles at MP minus :30.  (I do NOT advocate doing this, but perhaps finding some way to get that watershed moment late in the training cycle, but before the taper, of "I know 100% that I can run the intended pace for 26.2" is advisable.  That workout was not part of the Pfitz plan, it was me arrogantly flipping up pocket aces and pushing all my chips in after reading some Canova.)  I BQ'd with 6 minutes to spare.

I think that if the mileage for each cycle had been flip-flopped, but the meat of the training remained, the results wouldn't have changed.