Budget SIM Plans in Japan (格安SIM)

Why so many foreign residents overpay for their SIM

If you signed up for a phone plan at a docomo, au, or SoftBank shop in your first week in Japan, there's a good chance you're paying two to three times what you need to. The mainstream carriers still sell legacy plans that can run ¥6,000–¥8,000 a month for data most people don't use. The fix is switching to a 格安SIM (kakaku SIM, "budget SIM") — a catch-all term for the discount brands and MVNOs that run on the same physical towers as the big three but charge far less. This guide covers what a fair price actually looks like, how the switch works, and where the honest trade-offs are for foreigners specifically.

What you should actually be paying

Prices vary by provider, but as of 2026 the going rates (税込, tax included) cluster tightly enough to give you a benchmark:

• A light-use tier around 3GB should cost roughly ¥850–¥1,100/month.
• A heavier tier around 20GB should cost roughly ¥1,600–¥3,300/month.

If you're paying meaningfully more than that for similar data on a big-carrier plan, you're overpaying — full stop. For context on how a SIM plan fits into your broader connectivity setup (versus home fiber or a pocket router), see our overview of internet options in Japan for foreigners.

Example plans compared

Note: povo 2.0 has a ¥0 base plan and you buy data "toppings" on top as needed — good for very light or irregular use, less convenient if you want an automatic monthly renewal. Its 20GB topping option was discontinued in October 2025, so the 3GB and 30GB toppings above are the practical anchor points.

Two clusters: MVNOs vs. carrier sub-brands

The table above splits into two rough groups. IIJmio and mineo are classic MVNOs — they lease network capacity from the big carriers and tend to be the cheapest per GB, but capacity is shared, so speeds can dip during commute-hour peaks in busy areas. ahamo, LINEMO, and povo are online-only sub-brands run directly by docomo, SoftBank, and au — they cost a little more but ride on their parent's full-priority network, so speed and reliability are closer to a mainstream plan. Rakuten Mobile is its own case: a fourth full carrier with usage-based pricing, generally solid in cities and improving elsewhere.

Switching without losing your number: MNP

Keeping your existing phone number when you switch providers is called MNP (Mobile Number Portability), and there are two ways to do it:

1. Traditional MNP予約番号 (yoyaku bangou, "reservation number") — request this code from your current carrier (by app, phone, or in store), then enter it when signing up with the new carrier. The code is typically valid for about 15 days, so get it close to when you actually plan to switch.
2. MNPワンストップ (one-stop), available since May 2023 — skip contacting your old carrier entirely. You authenticate directly on the new carrier's site using your old carrier's ID and password plus your ネットワーク暗証番号 (network PIN), and the new carrier handles the transfer for you.

Switching itself is mostly free now — the ¥0 web release fee has applied broadly since 2021 — though a few full-service contracts still charge a signup or administrative fee, often around ¥3,850. Always check the new provider's fee page before committing.

Using a SIM as your home internet fallback

A data SIM can technically cover home internet through tethering if fiber installation is delayed or a landlord won't allow a router hookup. Treat it as a stopgap, not a long-term plan — per-GB cost adds up fast under heavy home use (video calls, streaming, remote work), and speeds are less consistent than a wired connection. If you're choosing between a mobile hotspot and a proper home setup, our home router vs. fiber comparison walks through the trade-offs, and the FAQ covers common setup questions for new arrivals.

Ready to switch SIM?