Why the cheapest-looking plan often isn't
Japanese fiber and mobile-home-router ads are built around a headline number: ¥0 construction, huge キャッシュバック (cashback), a router "free" for life. Almost none of that is false, exactly — but almost all of it is conditional on you staying put for two, three, or four years without changing your mind. If you compare home routers against fiber or shop internet options as a new arrival, the traps below are the difference between a plan that's actually cheap and one that just advertises cheap.
Trap 1: the 2-year term that renews itself
Most fiber contracts (2年契約 / 定期契約) run 24 months, and when that term ends, they don't just expire — they auto-renew for another 24 months unless you actively cancel. There's no grace period after the fact. Miss the window and you're locked in again, by default, with no email asking whether you meant to.
更新月: the only free exit
The penalty-free cancellation window is your 更新月 (koushin-tsuki, "renewal month") — typically a 3-month window covering the final month of your current term plus the two months after it. Cancel inside that window and you owe nothing extra. Cancel one day outside it, even by mistake, and two things happen at once: you're billed the 違約金, and the contract quietly rolls over for another two years.
Log into your provider's マイページ (My Page account portal) now and note your exact 更新月 dates. Set a reminder a few weeks before it opens — this is the single most useful thing you can do to avoid this trap.
Trap 2: the 違約金 amount depends on when you signed
The size of the cancellation fee isn't fixed — it depends on your contract's start date, because Japan's telecom regulator capped fees on newer contracts.
| Contract start date | Typical 違約金 (cancellation fee) |
|---|---|
| On or after 2022-07-01 | ~¥3,000–5,700 (capped near one month's fee) |
| Before 2022-07-01 (grandfathered) | ~¥9,000–20,000+ |
If you inherited a line from a roommate, took over a contract when moving into a share house, or have simply had the same fiber line for several years, don't assume the modern low cap applies. Check the original contract date in your マイページ — an old, grandfathered contract can cost several times more to exit than a fresh one.
Trap 3: "実質無料" construction is a loan, not a gift
実質無料 (jisshitsu muryou, "effectively free") is the phrase used for construction fees, and it's worth reading literally: "effectively," not "actually." The real construction cost — commonly ¥22,000–28,600 — is split into an installment over 24–36 months and offset by a matching monthly discount, so your bill nets out to roughly the same either way as long as you stay enrolled. Cancel before the installment finishes and the remaining, un-offset balance is billed to you as a lump sum on your final invoice. This is the same mechanism as the 違約金, running in parallel — you can owe both at once.
Trap 4: "free" routers work the same way
Home routers (ホームルーター) advertised as free follow an identical structure: the device's list price — commonly ¥33,000–95,000 depending on the model — is offset through monthly bill credits spread over roughly 48 months. Cancel or switch providers before those 48 months are up and you're billed whatever balance remains on the device. If you're weighing a router against a fixed fiber line, factor in how long you actually expect to stay in Japan before assuming the router is free.
Trap 5: cashback is a maybe, not a guarantee
Big advertised キャッシュバック numbers are real money providers do pay out — but the fine print makes them unreliable to plan around:
- Payment often arrives 6–12 months after signup, not at signup.
- You usually have to actively claim it, via a confirmation email sent to a separate provider-issued address you may rarely check.
- Miss the claim window — sometimes just a few weeks — and the cashback is forfeited entirely, with no reminder.
Treat cashback as a bonus if it lands, never as part of the baseline cost you're comparing between providers.
The honest way to compare plans
Skip the campaign math entirely and compute a 24-month true cost for each provider you're considering: monthly fee × 24, plus the standard (non-discounted) construction fee. Compare that number across providers. If a cashback or discount campaign actually pays out on top of that, it's a bonus — but the plan that wins on the true-cost comparison is the one that's actually cheaper, regardless of which one has the flashier ad.
Checklist: ask before you sign
- What is the exact contract term, and does it auto-renew?
- What are the specific 更新月 dates for this contract (not a general rule — the actual dates)?
- What is the 違約金 amount if I cancel outside the renewal window?
- Is construction genuinely waived, or is it an installment offset by a monthly discount that reverses if I leave early?
- If there's a router involved, is it truly free, or offset over ~48 months of bill credits?
- When and how do I have to claim any advertised cashback, and what happens if I miss that window?
If you're renting and haven't confirmed you're even allowed to run a fiber line into your unit, check apartment fiber permission before you sign anything. And if a specific term in a contract doesn't match what's described here, our FAQ covers more edge cases.
Find your internet options →