From injury to half / marathon

I've been running for about 18 months, built up to a base of 10-15 miles a week and had some reasonable race times (5k - 22, 10k - 46). I've been trying to build up to a half and a marathon. For the last month or so I've been injured and I probably won't be running at all for another 3-4 weeks. I'm trying to keep fit on the elliptical machine at the gym. Realistically could I be ready for a marathon in late April / early May if I don't start running again until say early Feb? I'm trying to match the time spent on the elliptical to the time I would spend running on a marathon plan

Realistically I'd say just possibly, if you were willing to run/walk the marathon, and if you were lucky and didn't get injured again during the training, but I really wouldn't advise it. I think you'd enjoy it (including enjoying the training and the race) much more and have less chance of injuring yourself again trying to ramp up the miles too soon, if you went for a spring half-marathon and an autumn marathon. For example (going by a couple of training schedules I have to hand), looking at a 16-week sub 3.45 marathon training schedule, it's starting at about 27 miles per week for week one... While the HM schedule I have used starts 10 weeks before the race at 13 miles per week, which sounds much more like where youre starting from.

A starting base of only 10-15 miles a week would be as much a concern to me as the injury recovery for running a spring marathon. If I was you I'd aim to up that to something like 25 miles a week as a base and then aim for an autumn marathon.

An injury, a low mileage base and a very short period to prepare is not a great way to prepare for your first marathon.

I'd echo the above.   If you were injury-free, with a current 10-15 mile base and targetted an early May race, you could do that.

But you're not injury-free...  and you cutting the training time to the bone by not starting for 3-4 weeks.

Definitely recommend looking to the Autumn.   There are plenty of running challenges you can take on in the shorter term.  Good luck with that injury.

Just in case its a typo in your posting (as it doesn't quite match the title), I'd say

- Marathon: no chance in Spring, Autumn would be fine.

- Half Marathon: I'd give yourself a minimum of twelve weeks from starting back until the event, but this is achievable.  You may need to adjust your target time, so don't expect to run the equivalent of your 10k PB over the distance (e.g. 46m 10k equals a sub 1:43 HM according to McMillan, so you may want to aim for a 1:50).

This is assuming you want to enjoy the events, and to run them - rather than to tick them off your personal to-do list. 

Thanks for your comments everyone.  I think the April marathon is probably dead in the water but I have another booked in October so need to focus on that instead.

#annoying!