100K Ultra Marathons
Step up to 100K and beyond on the trails of the Chiltern Hills and the Ridgeway National Trail, with generous cut-offs and full support.
Ready to go further?
A 100K is a big step up from a 50K. It's not just twice the distance. It means running through the evening and into the night, eating and drinking for 12 hours or more, and making good decisions when you're tired.
We organise two races at 100K and beyond, both on the trails of the Chiltern Hills and the Ridgeway, plus a 60K that makes the perfect stepping stone.
The Chiltern Hills 100K
The Chiltern Hills 100K is an anticlockwise loop from Chesham, taking in many of the best-known places in the Chilterns: the Ashridge Estate, Coombe Hill, Whiteleaf, Bledlow Ridge and Great Hampden.
There's around 1,800m of climbing, six checkpoints and a 19-hour time limit, so it suits runners stepping up to their first 100K as well as those chasing a fast time. The course records are 9:22:52 (men) and 11:24:18 (women), but the typical runner finishes in around 13 to 14 hours.
The Ridgeway Challenge – 139km
The Ridgeway Challenge follows the full 86 miles (139km) of the Ridgeway National Trail, from Ivinghoe Beacon to the Avebury Stones in Wiltshire, on a path that has been in use for over 5,000 years.
With a 28-hour time limit, most finishers run through the night. In 2026, the median finish time was 23 hours 40 minutes.
Building up to 100K: the Ridgeway Chase
Running alongside the Ridgeway Challenge, the Ridgeway Chase covers the first 60km of the trail, from Ivinghoe Beacon to Wallingford, with a 10.5-hour time limit.
It's the ideal race to bridge the gap between a 50K and your first 100K.
Compare our 100K ultras
Median times and finish rates are from the most recent edition of each race. Click a race for the full route, checkpoints and entry details.
| Race | Next date | Distance | Climb | Time limit | Median time | Finish rate |
|---|---|---|---|---|---|---|
| The Ridgeway Chase | Sat 29 May 2027 | 60k | 1000m+ | 10.5 hours | 8:03:42 | 83% |
| The Ridgeway Challenge | Sat 29 May 2027 | 86-miles / 139km | 1800m+ | 28 hours | 23:40:49 | 70% |
| Chiltern Hills 100K | Sat 2 Oct 2027 | 100k | 1800m+ | 19 hours | 13:54:46 | 87% |
The Ridgeway Chase
The Ridgeway Chase is a 60km point-to-point ultramarathon following the historic Ridgeway National Trail.
The Ridgeway Challenge
An 86-mile (139km) point-to-point trail running race along the entire length of The Ridgeway National Trail.
Chiltern Hills 100K
A 100K ultra marathon along the best and most loved trails within the Chiltern Hills.
Frequently asked questions
How long does it take to run a 100K ultra?
At the Chiltern Hills 100K, which has around 1,800m of climbing, the median finish time was 13 hours 20 minutes in 2025 and 13 hours 55 minutes in 2026. The winners finished in 9 to 10.5 hours, and the final finishers came in at around 18 hours. Most runners should plan for 12 to 18 hours on a hilly trail 100K.
What is the cut-off for the Chiltern Hills 100K?
There is an overall 19-hour time limit, with checkpoint cut-offs along the route. The race starts at 07:00, so most runners finish in the dark and must carry a head torch.
Is a 100K a good first ultra?
We'd recommend finishing at least one 50K or a long trail marathon first. A 100K means a lot more time on your feet, running in the dark and eating while you run. Our 50K races and the 60K Ridgeway Chase make good stepping stones.
How many people finish a 100K?
At the Chiltern Hills 100K, 87% of starters finished in both 2025 and 2026. At the 139km Ridgeway Challenge, 70% of starters finished in 2026.
Are your 100K races UTMB Index races?
Yes. The Chiltern Hills 100K and The Ridgeway Challenge are UTMB World Series Index races in the 100K category. The Ridgeway Chase is a 50K category Index race.
Can I have a crew or a drop bag?
Yes, we typically allow both of these at our long distance races. See each race page for full crew and drop bag details.
Explore more races
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50K ultra marathons
Four trail 50Ks with 9-hour time limits. The perfect first ultra.
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Chilterns trail races
Every race we put on in the Chiltern Hills, from 8K to 139km.
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Ultras near London
Ultras and trail races a short train ride from London.
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All ultra marathons
All of our ultra marathons, from 50K to 139km.
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I completed the ridgeway challenge this year (just about). The race benefits from a lovely route in a lovely area of the country. But what really made it stick out for me was how well organised it was, particularly on the day. The aid stations were great. The support provided was also amazing.
Jamie
The Ridgeway Challenge, 2025
Extremely well organised, such a great effort from all the staff and volunteers 👏
James
The Ridgeway Challenge, 2025
Keep up with the pace
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