01📱 Global vs. Japan: Opposite OS Structures
Start with the numbers. According to Statcounter GlobalStats data for August 2026, the global mobile OS share is Android 67.45% and iOS 32.52%. iOS holds a majority in the US (60.71%) and the UK (51.43%), while Android dominates in Germany (27.59% iOS) and India (7.17% iOS). Against this backdrop, Japan stands at iOS 64.95% — higher even than the US that month.
"65%" is a share of web traffic — by device, it is roughly 50/50
It is important to understand what Statcounter's numbers measure. Statcounter aggregates OS data from page views recorded on the sites that use its tracker, so the figure shows which OS generates more visits. It is not the ratio of device owners. It also swings from month to month: Japan's iOS share was 58.90% in June 2026, 63.59% in July and 64.95% in August (Statcounter).
Device-based surveys show a different picture. In MMD Research Institute's (MMD研究所) "September 2025 Smartphone OS Share Survey" (ages 18–69, n=34,414), the smartphone respondents mainly use was iPhone 48.3%, Android 51.4%. The institute's August 2026 survey (with the age range expanded to 18–79) found iPhone at 45.6%.
| Survey | iOS/iPhone share in Japan | What is counted |
|---|---|---|
| Statcounter (August 2026) | 64.95% | Web page views (usage) |
| MMD Research Institute (September 2025) | 48.3% | Main smartphone used (ages 18–69) |
| MMD Research Institute (August 2026) | 45.6% | Same as above (ages 18–79) |
The gap between the two suggests that iPhone users use the web more heavily, and that the iPhone share is higher among younger people and women. In MMD Research Institute's September 2025 survey, the iPhone share reached 81.0% among women in their 20s and 69.6% among men in their 20s. Depending on the target audience, the OS split you see in ad inventory can look like "roughly half" or "over 60%."
02🕰️ Historical Background: Why Japan Ended Up This Way
Japan's iPhone skew is usually explained by a combination of historical events and structural factors.
① SoftBank's early launch (2008)
The iPhone 3G went on sale in Japan on July 11, 2008, through SoftBank Mobile (SoftBank Mobile announcement, July 8, 2008). KDDI (au) began selling the iPhone with the iPhone 4S on October 14, 2011, and NTT Docomo with the iPhone 5s/5c on September 20, 2013 (company announcements). It took about five years for all three major domestic carriers to carry it, and during that period the iPhone established itself early as "the" smartphone — which is considered the starting point of today's structure.
② Carrier handset discounts and regulation
For many years, Japanese carriers sold handsets at deep discounts bundled with service contracts. The Ministry of Internal Affairs and Communications (MIC, 総務省) restricted this practice in stages: the amended Telecommunications Business Act (電気通信事業法), effective October 1, 2019, banned discounts conditional on continuing a service contract and, in principle, capped handset discounts at ¥20,000 (excluding tax). From December 27, 2023, the cap was revised to ¥40,000 in principle (MIC). The long period during which iPhones could be obtained cheaply under this discount environment is also thought to have boosted adoption.
③ High iPhone share among young people and women
MMD Research Institute's surveys show that the iPhone share is high among younger people, especially women. In the September 2025 survey it was 81.0% among women in their 20s, 73.7% among women aged 18–19 and 69.6% among men in their 20s. As this generation ages, the high iPhone share among young people may spread to older age groups.
03🔒 ATT Opt-In Rates: The Reality in Japan
Under Apple's ATT (App Tracking Transparency), apps on iOS 14.5 and later must obtain the user's permission to track them across other companies' apps and websites (Apple; applied to all apps from April 26, 2021). According to Adjust × Sensor Tower's "Mobile app trends 2025: Japan edition," Japan's ATT opt-in rate (the share of iOS users shown the permission prompt who granted it) went from 20.7% in H1 2024 to 21.4% in H1 2025. The global average published by Adjust is about 38% (Q1 2026), well above Japan. In a market where iOS accounts for such a high share of usage, this gap has a large effect on the absolute number of "trackable users."
In the same report, games have the highest rate at 31%, while finance is at 14.5% and entertainment at 16.9%. The basic ways to raise opt-in are an explanation screen shown before the permission prompt (a pre-prompt) and a purpose string on the prompt itself written specifically, in Japanese. A literal translation of English copy rarely gets across why users would benefit from granting permission.
04📊 From SKAdNetwork to AAK: Evolution and Implementation
Measuring ad performance for users who do not grant ATT permission falls to Apple's SKAdNetwork (SKAN) and AdAttributionKit (AAK), introduced in iOS 17.4. AAK is interoperable with SKAN and supports distribution through alternative app marketplaces as well as the App Store (Apple Developer). Because specifications differ significantly by version, the table below summarizes them based on Apple's documentation.
| Item | SKAN 3 | SKAN 4 | AAK (iOS 17.4+) |
|---|---|---|---|
| Number of postbacks | 1 (winning ad network only) | Up to 3 (iOS 16.1+) | Up to 3 |
| Conversion value | 6-bit (0–63) only | Fine (0–63) + coarse (low/medium/high) | Inherits fine + coarse |
| Measurement window | 24-hour timer that resets with each value update | Three windows: days 0–2, 3–7 and 8–35 | Three windows (attribution windows configurable from iOS 26) |
| Campaign identifier | Campaign ID (1–100) | Hierarchical source ID (up to 4 digits) | Hierarchical source ID (up to 4 digits) |
| Privacy protection | Privacy threshold | Crowd anonymity (tiers 0–3) determines how much data is returned | Similar tiered controls |
| Re-engagement measurement | Not supported | Not supported | Supported (iOS 18+) |
Source: Apple Developer Documentation (SKAdNetwork / AdAttributionKit; iOS & iPadOS 18 and 26 release notes).
In practice, two things are essential: plan for AAK support in any new implementation, and design a SKAN 4 conversion value schema. In particular, the fine value is included only in the first postback, so you need the design skill to pack buckets such as "day-one spend × level reached" into its 64 steps (0–63). Also build into your KPI design the fact that the second and third postbacks carry only a coarse value (three levels).
05🎯 Practical Impact on UA Planning
Japan's high iOS usage share and measurement constraints require the following changes to your operating logic.
① Switch to iOS-first operations
UA managers from countries with large Android markets tend, without thinking, to optimize on Android first and then expand to iOS. In Japan, reverse that order: design budget allocation and creative testing around iOS measurement constraints.
② Design creative tests for SKAN
Under SKAN 4, even the first postback arrives only after the measurement window (days 0–2) closes, followed by a further random delay of 24–48 hours (24–144 hours for the second and third postbacks). The decision window for creative tests needs to be extended to several days, rather than the traditional same day or next day. Android-style iteration — "judge after one day and pause" — does not work.
③ Limits of probabilistic attribution (PA) and device matching
Apple's developer agreement does not permit deriving data from a device for the purpose of uniquely identifying it (so-called fingerprinting) (Apple, "User Privacy and Data Use"). MMPs are divided on how they handle probabilistic attribution, and no single method covers most of Japan's iOS traffic. A combination of SKAN/AAK, incrementality tests and MMM (marketing mix modeling) is the realistic answer.
④ In-app bidding vs. waterfall
When buying inventory from ad networks, it is common to prioritize mediation platforms that support in-app bidding (AppLovin MAX, AdMob, etc.). Under iOS measurement constraints, bidding — which reflects bid information in real time — generally keeps the operational workload lower than manually tuning a waterfall.
06✅ Checklist for Launching iOS UA in Japan
- Confirm your MMP supports both SKAN 4 and AAK (Adjust / AppsFlyer / Singular, etc.)
- Design the conversion value schema starting from business KPIs (never use a template as-is)
- Optimize the ATT prompt's purpose string with specific Japanese copy plus a pre-prompt
- Extend the creative-test decision window to several days, allowing for postback delays
- Measure the actual OS split of your own target audience; allocate budget and optimize iOS-first, then roll out to Android
- Prioritize mediation that supports in-app bidding
- Run incrementality tests / MMM regularly to complement SKAN
Support from a conversion value schema built on business KPIs through to bucket design across all three postbacks.
MeasurementAcquire Japanese iOS traffic efficiently with a three-part package: performance-based (CPI) campaigns, in-app bidding and video creative.
Acquisition❓ FAQ
Why is the iPhone's share so high only in Japan?
What is the ATT opt-in rate in Japan?
What is the difference between SKAdNetwork and AAK?
What is the minimum preparation for iOS-first UA in Japan?
📚 Related articles
📖 Sources
- Statcounter GlobalStats, "Mobile Operating System Market Share," Worldwide / Japan / United States / United Kingdom / Germany / India (June–August 2026, accessed October 28, 2026)
gs.statcounter.com/os-market-share/mobile/japan - Statcounter GlobalStats, "FAQ" — methodology (based on page views on sites using Statcounter)
gs.statcounter.com/faq - MMD Research Institute (MMD研究所), 「2025年9月スマートフォンOSシェア調査」 [September 2025 Smartphone OS Share Survey] (October 21, 2025) — main device: iPhone 48.3%, Android 51.4%; iPhone share by gender and age
mmdlabo.jp/investigation/detail_2496.html - MMD Research Institute, 「2026年8月スマートフォンOSシェア調査」 [August 2026 Smartphone OS Share Survey] — iPhone 45.6%, Android 54.1% (ages 18–79)
mmdlabo.jp/investigation/detail_2567.html - SoftBank Mobile, 「7月11日のiPhone 3G発売について」 [On the July 11 launch of iPhone 3G] (July 8, 2008)
www.softbank.jp/corp/group/sbm/news/press/2008/20080708_01 - KDDI / Okinawa Cellular, 「au初となるiPhoneを10月14日より発売」 [au's first iPhone to go on sale October 14] (October 7, 2011)
www.kddi.com/corporate/news_release/2011/1007b/ - NTT Docomo, 「NTTドコモ、9月20日より『iPhone 5s』『iPhone 5c』を発売」 [NTT Docomo to launch iPhone 5s and iPhone 5c on September 20] (September 15, 2013)
www.docomo.ne.jp/info/news_release/2013/09/15_00.html - Ministry of Internal Affairs and Communications (MIC, 総務省), 「電気通信事業法の一部を改正する法律の施行に伴う関係省令等の整備について」 [Ordinances related to the enforcement of the amended Telecommunications Business Act] (June 2019) — effective October 1, 2019; handset discount cap of ¥20,000 (excluding tax)
www.soumu.go.jp/main_content/000628680.pdf - MIC, 「電気通信事業法施行規則等の一部改正の概要」 [Overview of amendments to the Ordinance for Enforcement of the Telecommunications Business Act] (November 2023) — handset discount cap revised to ¥40,000 in principle (effective December 27, 2023)
www.soumu.go.jp/main_content/000913308.pdf - Adjust × Sensor Tower, "Mobile app trends 2025: Japan edition" (July 2025), p.5 — Japan ATT opt-in rate 20.7% (H1 2024) → 21.4% (H1 2025); values by category
a.storyblok.com/f/47007/x/9682af56e4/japan-app-trends-2025.pdf - Adjust, "Mobile App Trends 2026" (February 18, 2026) — global average ATT opt-in rate of 38% (Q1 2026)
www.businesswire.com/news/home/20260218837408/en/Adjust-Mobile-App-Use-Grew-Globally-In-2025-With-Continued-Move-To-Multi-Platform - Apple Developer News, "Upcoming AppTrackingTransparency requirements" — ATT applied to all apps from April 26, 2021
developer.apple.com/news/?id=ecvrtzt2 - Apple Developer, "User Privacy and Data Use" — ATT permission on iOS 14.5 and later; prohibition on deriving data to uniquely identify a device
developer.apple.com/app-store/user-privacy-and-data-use/ - Apple Developer Documentation, "Receiving postbacks in multiple conversion windows" — SKAN 4 number of postbacks, measurement windows and sending delays
developer.apple.com/documentation/storekit/receiving-postbacks-in-multiple-conversion-windows - Apple Developer Documentation, "Identifying the parameters in install-validation postbacks" — fine/coarse values, crowd anonymity (tiers 0–3), hierarchical source IDs
developer.apple.com/documentation/storekit/identifying-the-parameters-in-install-validation-postbacks - Apple Developer Documentation, "adCampaignIdentifier" — campaign ID (1–100) in SKAN 3 and earlier
developer.apple.com/documentation/storekit/skadimpression/adcampaignidentifier - Apple Developer Documentation, "AdAttributionKit" — introduced in iOS 17.4; supports alternative app marketplaces; interoperable with SKAN
developer.apple.com/documentation/adattributionkit - Apple, "iOS & iPadOS 18 / 26 Release Notes" — AAK re-engagement (iOS 18), configurable attribution windows (iOS 26)
developer.apple.com/documentation/ios-ipados-release-notes/ios-ipados-26-release-notes