Training for your first marathon? Here’s how to go from half to full in 12 weeks – just in time for Kielder

Altra Kielder Marathon 2025 is on the horizon – and if you’ve ticked off a half marathon or two and are thinking about the next big challenge, this is your sign. Because yes, you can go from half to full in 12 weeks – and there’s no better place to do it than Kielder.

Twelve weeks from now, you could be standing at the start line on the shores of northern Europe’s largest man-made lake, ready to take on 26.2 miles of pure inspiration.

It’s a big goal. But with the right approach, the right training and the right event… it’s absolutely achievable.

Why go for your first marathon at Kielder?

Because it’s one of the most breathtaking races in the UK.

It’s known as Britain’s Most Beautiful Marathon for a reason – Kielder takes you on a full lap of the stunning lake through forest trails and epic views, with the support of fellow runners and the satisfaction of a real adventure completed.

It’s wild, it’s peaceful, it’s tough but rewarding… and it’s something you’ll never forget.

Whether you’re a North East local or travelling in for the weekend, Kielder is a chance to test yourself, take in the scenery and soak up the pride of completing all 26.2 miles.

Can I go from half to full marathon in 12 weeks?

Yes – if you’ve already run a half marathon (even if it was a while ago), you’ve got the base fitness to build towards a full. It’s not about doubling everything overnight – it’s about slowly increasing your long runs, building strength and getting your body used to longer efforts.

Before you start, it’s always smart to get a quick check-in with a physio or GP, especially if you’ve had any niggles in the past. And if you’re not sure what to do week by week, working with a coach of following a simple plan can help massively.

As Kielder is a trail event, we recommend getting a pair of trail shoes to train and race in. It’s important to make sure you’ve tested everything you’re going to wear on race day, to avoid any surprises and discomfort. Our title partner, Altra, are specialists in trail shoes, pioneering a FootShape Toe Box and Zero to Low Drop, designed to keep you comfortable and more the way you were designed to. Visit the Altra website to browse the range and treat yourself before race day!

Here’s a straightforward example to guide you through the next 12 weeks:

Your 12-week half-to-full marathon plan

Weeks 1-4: Build the base

• At least 3-4 runs per week
• Long run = start at 14 miles and build up by 1 mile per week
• Midweek = 1 easy run, 1 steady/moderate pace run, 1 optional short run or cross-training
• Focus on building routine and running on tired legs

Weeks 5-8: Extend endurance

• Long runs increase from 18-20 miles (every other week)
• Cut back weeks in between to recover (e.g. drop to 14-15 miles)
• Add in some marathon pace efforts during long runs (e.g. final 3-5 miles at goal pace)
• Stay consistent and don’t neglect recovery

Weeks 9-10: Peak

• Longest run in week 9 (10-21 miles)
• Reduce overall volume slightly in week 10
• Keep intensity moderate – the goal is to arrive at the taper feeling strong, not exhausted

Weeks 11-12: Taper

• Drop mileage by ~30-40%
• Do one or two fewer runs per week, and make them shorter and easier
• One short ‘long run’ (e.g. 8-10 miles) the week before
• Focus on sleep, nutrition, hydration and mental prep
• Don’t overdo it – trust your training

Top tips for first-time marathoners

• It’s not just double a half – it’s a different beast, so pacing and fuelling matter. Learn what works for your body on long runs.
• Slow down to go long – Your long runs should be slower than race pace. They’re about time on your feet, not speed.
• Practice race day in training – Try out your kit, shoes, fuelling and hydration during your long runs.
• Respect the rest – Recovery days are part of the plan. They help you get fitter, not lazier.
• Keep your head strong – There will be tough runs. That’s normal. Keep showing up and trust the process.

Why now?

Because in 12 weeks from now, you could cross the finish line of one of the UK’s most iconic marathon courses. If you’ve been wondering whether this is the year you finally go the distance – Kielder is calling!

Get your name on that start list and start your journey to 26.2. Sign up for Kielder Marathon 2025.