Your ahamo plan may already have 10GB more.

1. Check what changed on August 1

ahamo's official FAQ says the Data Increase Trial started August 1, 2026. During the trial, the regular plan receives 10GB on top of its normal 30GB, while a line with the Large Data option reaches 120GB instead of the normal 110GB.

• The monthly price remains ¥2,970 for the 40GB trial allowance.
• With the Large Data option, the total remains ¥4,950 for 120GB during the trial.
• The extra 10GB is applied automatically to an ahamo line active during the campaign; no campaign entry is required.
• JAL Mobile powered by ahamo users are also included while they meet the stated plan condition.

2. Choose 40GB or 120GB by the job, not the headline

For a resident using a Japanese number and carrier SMS, 40GB can add breathing room for commuting, maps, school portals, work chat, video calls, and the weeks before home Wi-Fi is ready. The 120GB route still requires the paid Large Data option, so choose it only when tethering, remote work, classes, or streaming justify the monthly total.

• Choose 40GB if ordinary phone use plus moderate video fits without repeated extra-data purchases.
• Consider 120GB when a phone hotspot replaces unreliable home or dorm Wi-Fi for a meaningful part of the month.
• The trial does not turn Large Data into a free option; it changes the available data, not the listed ¥1,980 add-on price.
• If maps, translation, and messaging are all you need for a short visit, compare a visitor data eSIM instead of opening a resident monthly line for this trial.

3. Treat 40GB and 120GB as temporary monthly allowances

The official campaign page shows a start date but no end date. It also says allowances return to the normal 30GB or 110GB after the trial. Budget and choose the plan on those normal figures rather than assuming the extra 10GB will continue.

• There is no published closing date to count down to as of August 9; check the official FAQ before applying or changing options.
• Unused ahamo data does not roll into the next month, including when the Large Data option is active.
• Use the ahamo site or app to monitor the current month's consumption and remaining allowance.
• If 30GB is normally enough, do not add Large Data only because the temporary 120GB number looks larger.

4. Keep the overseas decision at 30GB

The extra domestic 10GB does not raise ahamo's overseas allowance. The official roaming page still caps monthly overseas data at 30GB, including for Large Data users, and applies a separate speed rule after more than 15 days abroad.

• Check that the destination is in ahamo's current supported-area list before departure.
• After 15 days from the first overseas data use, overseas speed is limited to a maximum 128kbps from 00:00 Japan time until the line reconnects to data in Japan.
• Buying more data does not remove that 15-day restriction while you remain abroad.
• Keep voice, carrier SMS, 2FA, and data-roaming costs as separate checks; extra domestic data is not an overseas calling or SMS benefit.

5. Decide on the normal plan, then take the trial as upside

The safest order is resident-line need → normal 30GB or 110GB fit → device, identity, and payment readiness → current trial status. That protects the Japanese number and SMS tasks you actually need if the trial ends.

• Compare the underlying plan in the ahamo 30GB and 110GB guide before sizing the temporary allowance.
• If travel is part of the decision, use the resident roaming comparison and keep the 30GB overseas ceiling in view.
• Check alternatives on the plans page and confirm phone-number, SMS, setup, and 2FA limits in the FAQ.
• This site includes referral links. Use the referral page only after the live official plan, trial, identity, device, payment, and application conditions match your route.