Phone Signal on Mount Fuji: Trails, Huts and Summit

It's 4:30 in the morning, you're standing on the crater rim at 3,776 metres, the sky is turning orange, and you want to send that photo to your mum before your hands get too cold to type.

Good news: it will probably go. All three Japanese carriers put 5G on the summit of Mount Fuji during the climbing season, and 4G runs along all four trails.

The catch is the word season. The antennas that make the summit work are temporary. They go up in July and come down at the end of August — while the trails themselves stay open until 10 September. Climb in that last stretch and you're on a quieter mountain in every sense.

📶 What the carriers actually put on the mountain

Here's the thing most people don't realise: Mount Fuji's network is seasonal furniture.

SoftBank explains on its own news site that the base stations sit on mountain huts and the old weather station at the summit, and that power comes from the huts' generators — which makes electricity, in their words, an extremely precious resource. No huts running, no power, no signal.

KDDI has been doing this since 2009 and now runs 5G SA at the summit and at the Gotemba new 5th station, on top of year-round 4G LTE at the trailheads and along all four routes. docomo covers the summit around Kengamine with 5G and 4G, and the trails and huts with 4G. SoftBank does the same, and added Sub6 and 5G SA at the summit for the 2026 season — though it says plainly that the 5G area is only part of the summit.

The seasonal dates for 2026 tell the story:

Look at the last two rows together. There's a gap of roughly two weeks at the end of the season where you can legally climb but the top-end kit is being packed away. Honestly, this is the single most useful thing on this page. If signal at the summit matters to you — because someone at home is tracking you, or because you're solo — climb in the middle of the window, not at the edge of it.

Roaming on an eSIM or a travel SIM? You ride on whichever Japanese network your plan uses, so the coverage above is your coverage too. There's nothing Fuji-specific to buy.

🧭 Coverage by trail, from 5th station to summit

All four routes have year-round 4G LTE at the trailhead and along the trail, according to KDDI's and SoftBank's own service pages. What changes between routes is how much else you get.

Two honest caveats from the carriers themselves. SoftBank says signal disappears if you leave the marked route, and that terrain can put you in an antenna shadow even on it. KDDI's engineers pay particular attention to the ohachi-meguri crater rim loop at the top — the walk right round the crater takes you behind the summit's bulk, and that is exactly the sort of place a beam-shaped mountain signal doesn't reach.

My read: Gotemba is the route where I'd assume the most dead ground. It's the longest trail with the fewest huts, and since the huts are what hold the base stations, the gaps between them are simply bigger.

📱 Wi-Fi and plug sockets in the huts

This part has genuinely changed in the last couple of years, and older advice online is out of date.

Free Fujisan Wi-Fi runs at 48 locations around the mountain, including huts, in 14 languages, from early July to early September. Separately, KDDI and Wi2 run satellite-based Wi-Fi via Starlink at 29 huts, which KDDI's release puts at up to 220 Mbps. Free for au users; other carriers pay.

Look at the service's own hut map, though, and the listed huts cluster heavily on the Yoshida route — Satō-koya, Tōyōkan, Kamaiwakan, Taishikan, Hōraikan, Ganso-shitsu, Goraikōkan and more. If hut Wi-Fi is part of your plan, Yoshida is the route that delivers it.

Charging is hut by hut. Kamaiwakan, at the 7th station on the Yoshida trail at 2,790 m, says on its own FAQ that every sleeping space — dorms included — has a socket at the pillow, and that its Starlink Wi-Fi costs a few hundred yen for 24 hours (as of 2026-09). Tōyōkan, a little higher on the same trail, says each room has its own light and socket, with free Wi-Fi in the hall.

That same Kamaiwakan FAQ is unusually candid about signal: docomo and au LTE work fine there, it says, while SoftBank can be unstable. A hut telling you which carrier struggles at its own altitude is the most specific coverage information anywhere on this mountain.

Still, assume nothing. Book a hut, then check that hut's own page.

🔋 Cold, thin air and a battery that quits early

Japan Meteorological Agency 30-year normals for the Fuji summit station put the August mean at 6.4°C, with an average daily low of 3.8°C. September drops to a 3.5°C mean and a 0.6°C average low.

Translate that: you are standing still, in the dark, in wind, at roughly November-in-Tokyo temperatures, waiting for sunrise. Phone batteries hate it. A phone showing 60% at the 8th station can shut down within minutes of being pulled out of a warm pocket at the top.

Three things fix most of it.

Carry a power bank and keep it inside your jacket, not in your pack. Same for the phone between uses.

Buy a couple of kairo — the stick-on heat pads sold in every convenience store and pharmacy in Japan. One in the pocket with your phone keeps it working.

And put the phone in airplane mode on the stretches where you don't need it. Hunting for a signal in an antenna shadow is one of the fastest ways to drain a battery on the mountain.

🎟 The permit system now assumes your phone works

Since 2026, every climber on every trail pays ¥4,000 (as of 2026-09), and the way you prove it is digital.

On the Shizuoka side — Subashiri, Gotemba, Fujinomiya — you register through the prefecture's FUJI NAVI app, watch a short rules video, take a test, and get a QR code entry permit to show at the gate. The app also pulls your GPS position inside a 7 km radius of the summit for safety purposes, and pushes weather and emergency alerts, which means it wants to run in the background the whole climb. That's a real battery cost — plan for it.

On the Yamanashi side, the Yoshida trail is capped at 4,000 climbers a day and booked through the prefecture's official system. Both sides shut their gates from 2 p.m. to 3 a.m. unless you have a hut booking.

The FUJI NAVI app itself gets a mixed reception. Reviews on its App Store page complain that you pay the fee on a separate website while the app only handles the e-learning and displays the permit, and that you end up creating two accounts — one for the app, one for the payment site. One two-star review sums it up: payment is card or a few pay services only, so anyone else has to sort it out on the spot on the day.

So do the boring thing. Register at home on hotel Wi-Fi, screenshot your QR code, and don't rely on a signal at the gate.

❓ Quick questions

Will my foreign eSIM work at the summit?
If it roams on docomo, au or SoftBank, yes — in season. The coverage is the host network's, not something extra you buy.

Can I livestream the sunrise?
The summit has 5G in season, and SoftBank specifically upgraded it for heavier uploads in 2026. But it's part of the summit, thousands of people are there at once, and it's freezing. Send a photo, enjoy the sky.

Is there signal off-season, in October or May?
The trails are officially closed and the summit kit is gone. The year-round 4G along the routes is what's left, with gaps. This isn't the time to count on your phone.

Do I need a paper map as well?
It's a sensible backup. Yamanashi offers a free Mt. Fuji GPS app that gives voice alerts if you wander off route, but a dead battery ends any app.

Which trail is best if staying connected matters?
Yoshida. Most huts, most hut Wi-Fi, most charging sockets, and the trail is busy enough that help is never far.

🧳 Before you go

• Mount Fuji has proper 4G and 5G — but the summit equipment is seasonal, roughly early July to late August
• The trails stay open to 10 September; climb the middle of the window if signal matters
• Yoshida has the most huts, the most Wi-Fi and the most sockets
• Cold kills batteries: power bank inside your jacket, a heat pad in the same pocket, airplane mode between checks
• Your entry permit is a QR code — register before you travel and screenshot it

Next step: book your hut first, then open that hut's own website and check what it says about sockets and Wi-Fi. It's a two-minute job that decides whether your phone survives to sunrise.

Sources

• 今年も富士山の山開きに合わせて快適な通信環境を提供します（Mt. Fuji seasonal coverage） — NTT docomo (accessed 2026-09-11)
• 富士山頂と御殿場口新五合目で5G SAを提供 — KDDI (au) (accessed 2026-09-11)
• 富士山頂で「SoftBank 5G」を提供 — SoftBank (accessed 2026-09-11)
• 電波きてます！ 毎年進化する夏の富士山の電波対策 — SoftBank News (accessed 2026-09-11)
• 標高3,776mでau 5Gがつながる！安心・安全な富士登山のためのKDDIの取り組み — KDDI Spark Journal (accessed 2026-09-11)
• 富士山頂と御殿場口新五合目で5G SAを提供（富士山Wi-Fi・山小屋Wi-Fi） — Wire and Wireless (Wi2) (accessed 2026-09-11)
• Starlinkを活用したau Starlink 山小屋Wi-Fi 設置山小屋一覧 — Wire and Wireless (Wi2) (accessed 2026-09-11)
• Yamanashi Prefecture Mt. Fuji climbing notice (Yoshida Trail) — Official Web Site for Mt. Fuji Climbing / Yamanashi Prefecture (accessed 2026-09-11)
• Shizuoka Prefecture Mt. Fuji climbing notice 2026 — Official Web Site for Mt. Fuji Climbing / Shizuoka Prefecture (accessed 2026-09-11)
• Things you must know before climbing Mt. Fuji — Official Web Site for Mt. Fuji Climbing (accessed 2026-09-11)
• SHIZUOKA FUJI NAVI アプリ利用マニュアル — Shizuoka Prefecture (accessed 2026-09-11)
• 静岡県 FUJI NAVIアプリ (App Store listing and user reviews) — Apple App Store / LECIP Corporation (accessed 2026-09-11)
• 富士山吉田ルート七合目 鎌岩館 よくある質問 — Kamaiwakan mountain hut (accessed 2026-09-11)
• 海抜一万尺 東洋館【公式】 — Toyokan mountain hut (accessed 2026-09-11)
• 富士山 平年値（月ごとの値） — Japan Meteorological Agency (accessed 2026-09-11)