Cross-Platform Budget App — Android, iPhone and Web in 2026

You're on an iPhone, your partner's on Android — or your teenager just inherited an old Galaxy. The app has to work on every device, and the numbers have to match. A web client is what makes it real.

Adam Przywarty

martia.ai

May 2026|11 min read

Most budget app round-ups assume a single user with a single phone. That isn't the real world. In a typical European household, one person uses Android, another uses iOS, and a laptop is somewhere in the mix. The question isn't which app is "best". It's whether the same app actually runs on both phones and whether the data matches across devices.

A cross-platform budget app is one that ships a client for Android, iOS and the web, with all three reading from one shared cloud database. Mobile-only isn't enough if you replace your phone every three to four years or share finances with someone on a different OS. This piece compares seven apps available across Europe under that lens — plus the specific traps you won't see in standard rankings.

Key takeaways

In Europe, Android holds roughly 71% of mobile and iOS roughly 29% (StatCounter, 2026) — basic probability puts random couples at ~41% odds of mixed-OS
Banking apps (your bank's own app) ship on both systems, but each only shows transactions from its own bank
Many finance apps have full feature parity on only one OS — widgets, smartwatch integration, biometrics
A web client as a third equal surface solves most cross-platform problems — Martia ships one alongside its mobile apps
Local-only apps (no cloud account) require manual export every time you change phone — choose apps with server-side sync

Why a budget app on Android and iPhone isn't a detail

A mixed-OS household is a family or couple in which at least one person uses Android and another uses iOS. It is not an edge case. According to StatCounter (2026), Android holds around 71% of European mobile market share against iOS at around 29%. Two randomly paired people therefore have roughly a 41% probability of running different operating systems — often higher in practice, because iOS clusters in particular demographics and Android in others.

The other side of the equation: people switch phone systems. A decade on Android, then a MacBook, then an iPhone. Or a long iOS run ended by one flagship Galaxy and that's it. Every such migration is a test of whether your budget history survives the device change. Apps that stash everything in local storage lose at this game.

What actually breaks when an app is only "technically" cross-platform

Each of these is a real shortcoming in apps that nominally exist on both systems:

• Features shipped on one OS only (lock-screen widget, Apple Watch, Wear OS)
• Different API versions — Android gets a new feature, iOS waits on App Store review
• Local database instead of cloud — you lose history when you change devices
• A subscription bought on iOS doesn't apply on Android, and vice versa (separate platform billing)
• No web client — zero access from a laptop, no browser-based backup

For a broader view of household budgeting apps across Europe, start with our best household budget app comparison — this article narrows the question to cross-platform.

Three scenarios where cross-platform is mandatory

A cross-platform finance app isn't a luxury for tech-curious users. It's the minimum requirement in three common household situations. If you recognise any of them, mobile-only apps are off the table from the start.

Scenario 1: a mixed-OS couple

The most common case. You're on iOS, your partner's on Android — or the other way around. Shared rent, shared groceries, one yearly holiday. For the budget to actually be shared, both of you have to see the same numbers. An app that doesn't exist on one of your systems collapses into one person controlling the household finances — which rarely ends well for the relationship or the budget.

Scenario 2: switching Android ↔ iPhone

You're moving from Android to iOS or vice versa. This is the classic trap of local apps — all of your spending history is on the old device. Without a cloud account, there's no one-click transfer. CSV export usually rescues you, but only if you remember to do it BEFORE handing back the old phone.

Scenario 3: a family with a teenager on an old phone

A teenager inherits an older Galaxy or iPhone, gets pocket money, starts tracking small spending. Parents are on a different system. A shared family budget has to run on three devices at once — parent on iPhone 15, the other parent on a Pixel, child on a tired Samsung. Without cross-platform plus a web client, you end up with three disconnected apps and zero shared truth.

What 'cross-platform finance app' actually means

A cross-platform finance app is one that ships native clients on Android and iOS plus a fully featured web client, all three pulling from the same cloud database. The defining property: changing devices does not require data migration — you sign in on the new device and the history is there.

Mobile context across Europe — 2026

~71%

Android mobile market share in Europe (StatCounter, 2026)

~29%

iOS mobile market share in Europe (StatCounter, 2026)

~41%

math-based probability of a mixed-OS pair across Europe

finance-app retention after 30 days in Europe (AppsFlyer, 2025)

Sources: StatCounter GlobalStats 2026, AppsFlyer Europe Finance App Trends 2025

Cross-platform budget apps compared — 7 options for 2026

The table below compares seven apps on the dimensions that actually matter when a household has more than one phone: presence on both systems, web client, sync model, multi-user support and what happens during migration. As of May 2026.

App	Android	iPhone	Web app	Cloud sync	Shared household	Migration
Martia	Yes	Yes	Yes	Real-time	Couple dashboard	No export needed
YNAB	Yes	Yes	Yes	Real-time	Yes (shared login)	No export needed
Spendee	Yes	Yes	Yes (Premium)	Yes (Premium)	Yes (Premium)	No export needed (Premium)
Wallet by BudgetBakers	Yes	Yes	Yes (Premium)	Yes (Premium)	Yes (Premium)	CSV (free tier)
Emma (UK)	Yes	Yes	No	Cloud (account)	No	No export needed
Finanzguru (DE)	Yes	Yes	No	Cloud (account)	No	No export needed
Monefy	Yes	Yes	No	Local (free)	No	Manual CSV

Three columns reshape the picture compared to a standard ranking: Web app, Cloud sync and Migration. Without a web client you lose laptop access. Without cloud sync, switching devices is painful. Without multi-user support, the app isn't usable for couples. Most European apps fall short on at least one of these — Martia and YNAB cover all three, with the difference that Martia connects directly to European banks through PSD2 and runs in multiple languages.

For a deeper view of which apps connect to which banks across Europe, see our piece on automatic expense categorisation in personal finance apps.

Different banks, different phones — one shared view

Martia runs in parallel on Android, iOS and the web — all three backed by the same database. Add a transaction manually on the iPhone, see it on the Android within seconds. No spreadsheets, no exports.

Try Martia for free →

Cross-platform pitfalls the store listing won't tell you about

The app store will tell you whether an app exists on both systems. It won't tell you whether it works the same way on both. Five common asymmetries worth checking before you drag a partner into a new tool.

Widgets exist on only one system

Apple introduced lock-screen widgets with iOS 16; home-screen widgets have been there since iOS 14. Android has had them for over a decade in a different format. Many developers ship a widget on one platform first and leave the other for later. If you want to glance at a balance without unlocking your phone, check the widget availability for your specific OS.

Apple Watch vs. Wear OS — often missing on one side

An app may have a dedicated Apple Watch companion (quick expense entry from the wrist) but nothing on Wear OS — or the other way round. A small feature in absolute terms, but a disproportionately large gap if your smartwatch is part of your daily flow.

Different update cadence

Apple's App Store requires code review on every release (usually 24-72 hours). Google Play ships patches faster. Minor bugs can persist on iOS longer than on Android — an asymmetry you won't spot in the store listing, but one you'll feel during an incident.

A subscription bought on iOS doesn't carry over to Android

Paid plans billed through the App Store and Google Play are two independent billing rails. Buy Premium on iPhone, switch to Android, and the iOS subscription stays where it was. The user account typically retains its premium status (when the app has its own user system), but cancelling and re-purchasing on Android is a separate operation. Apps that bill through their own website (such as YNAB) bypass this entirely.

Local database instead of cloud

The most dangerous trap. The app works, transactions go in, everything looks great — until the device dies or you sell it, and the data is gone. CSV export rescues you only if you remember to do it BEFORE. If the app requires a user account (email and password) and syncs to a server, this whole class of problem disappears.

Myth vs. reality

Myth: "If the app is in both stores, it works the same way on both systems."

Reality: Functional parity between the iOS and Android versions of the same app can diverge by 20-30%. Widgets, smartwatch integration, biometrics, offline mode, export format — these are all areas where one side often leads the other by months. Verify the specifics for your OS before rolling out the app across the household.

What Martia does differently across systems

Martia was built in 2026 as an app where you talk to an AI assistant about your money — you can read more about that angle in our piece on how automatic expense categorisation actually works. For this article, three deliberate technical choices matter, because they solve the cross-platform problem directly:

Web client as a peer, not a fallback

The Martia web app has the same surface as the mobile clients — chat, dashboard, transactions, settings, export. It isn't a cut-down landing page or a sign-in form. It's the third full client, the one you reach for from a laptop when planning the month and you don't want to do it on a phone screen. It's also the recovery scenario: if you lose a phone, the web client gives you access immediately from any browser.

One mobile codebase — Flutter

The Martia mobile app is built in Flutter — one codebase, two output bundles (Android APK and iOS IPA). The practical consequence: new features land on both systems together rather than as a staggered rollout. The "iOS gets it first, Android follows in a month" asymmetry is reduced here to whatever the App Store review takes (typically 1-3 days).

One database — no local copies

All three clients (Android, iOS, web) query the same cloud database. There is no local copy of your transactions on the phone. Upside: switching devices is a clean login. Downside: you need internet to open the app. That's a deliberate trade-off — for a finance app, consistency across devices matters more than an offline mode in airplane seat 24A.

Adam, założyciel Martia

From the founder

I use a Pixel; my co-founder Bart uses an iPhone. While we're building Martia, we test everything on both systems daily. When something looks off on one OS, we see it within 24 hours, not after release. That isn't a marketing claim — it's a consequence of the actual setup we develop in.

The Three-Device Test — how to verify an app is really cross-platform

The Three-Device Test is a simple method for checking whether an app actually ties three clients into one coherent view — before you commit a partner, child or the whole household to it. The full test takes five minutes.

1. Install on three devices

Phone A (Android), Phone B (iPhone), laptop (browser). Create one account — email and password. Sign in on each of the three.

2. Add a transaction on each separately

On Android, log a transaction "test Android €5". On iPhone, "test iPhone €7". On web, "test web €3". Different amount and name on each, so you recognise them.

3. Check consistency after 60 seconds

Open each device. You should see all three transactions in the same place, in the same order, with the same amounts. If anything is missing on one device or requires a "pull to refresh" to appear, the app isn't truly real-time.

4. Delete one and repeat

Delete "test iPhone €7" from the web client. Check both phones — it should disappear from both within seconds. If it lingers on one device, the app isn't cross-platform in the meaningful sense. It's three separate copies that synchronise inconsistently.

I use the same test whenever someone asks if a specific app fits a couple with different phones. If it fails the Three-Device Test, it's out. Data consistency is the foundation of a shared budget — without it, both people are looking at slightly different truths.

Android ↔ iPhone migration — how not to lose your history

A device migration between systems is the moment when every shortcut taken during app design shows up. Three paths, ordered from least to most painful.

Path A: cloud account (Martia, YNAB, Spendee Premium)

The simple case. Install the app on the new phone, sign in with your email and password, see everything immediately. You can even skip the old phone entirely — the data lives on the server. Migration time: two minutes.

Path B: export-to-file (Monefy, EasyBudget, Wallet free tier)

Workable, but takes effort. Step 1: on the old phone, open the app → Settings → Export (usually CSV or a proprietary backup format). Step 2: send the file to yourself (email, cloud, Bluetooth). Step 3: on the new phone, open the app → Settings → Import. Critical: do this BEFORE resetting the old device. Migration time: 10-20 minutes.

Path C: no cloud, no usable export

This is where it gets ugly. Some older finance apps store everything locally and don't ship a sensible export. The only option is to manually re-enter your history (almost nobody does) or to start over on the new phone. If you're shopping for an app and Path C applies to your current one — treat that as a strong signal to migrate to something with a cloud account before the phone itself fails.

Whichever scenario applies, also check the implications for bank account synchronisation through PSD2. PSD2 currently requires re-authorisation every 90 days, so a new phone is a good time to refresh consent for all banks at once.

Run the Three-Device Test on Martia in 5 minutes

Install on Android, iPhone and your laptop browser. Add three test transactions from different devices. Everything should be consistent in seconds — no manual refresh, no waiting, no export.

Try Martia for free →

Quick recommendation — cross-platform

→ Mixed-OS couple, European banks: Martia — Android, iOS, web, real-time sync, chat-first AI, free
→ If you want YNAB methodology: YNAB — all three clients, real-time sync, around €15/month, US-centric bank coverage
→ UK-only households: Emma — Android, iOS, cloud, but no web client and no household account
→ DE-only households: Finanzguru — strong on German banks, but mobile-only
→ If neither of you ever changes phone: your bank's own app (Revolut, N26, Monzo) — free, works everywhere, but only that one bank

Frequently asked questions

Which budget app works on Android and iPhone?

Apps that publish a client for both systems include Martia (Android, iOS and web), YNAB, Spendee, Wallet by BudgetBakers, Emma, Monefy and Finanzguru. The critical difference is whether they also offer a web client. Martia, YNAB and Wallet (Premium) have full web access — most other apps are mobile-only, which becomes a problem when you switch phone systems or want to plan budgets from a laptop. For a broader view of household budgeting tools, see our best household budget app comparison.

Does a cross-platform budget app sync data between phones?

Only if the app uses a cloud-based account. Local-only apps (Monefy free, Wallet without Premium) keep data on the specific device — moving to a new phone requires manual export and import. Apps with a user account and server sync (Martia, YNAB, Spendee Premium, Wallet Premium) keep data on the server — sign in on the new device and everything is there.

What does cross-platform mean in a finance app?

Cross-platform in this context means three things: (1) native client on Android, (2) native client on iOS, (3) full web access from any browser, all three reading and writing to the same cloud database. Apps that only have Android and iOS — without a web client — fail the test for households where one person uses a laptop heavily, or where someone temporarily loses access to their phone.

How do couples sync budgets when one has Android and the other an iPhone?

Pick an app that supports either a shared household account or two linked accounts feeding one dashboard. Both partners sign in on their preferred OS, transactions from both bank accounts (typically connected through PSD2 Open Banking in Europe) land in the same view, and neither person has to switch their phone or their bank.

What happens when I switch from Android to iPhone (or vice versa)?

If the app uses a cloud account: install it on the new phone, sign in, everything appears immediately. If the app stores data locally: you must export (usually CSV) on the old phone before resetting it, then import on the new one. Banking apps themselves are unaffected because the transaction history lives at the bank — only third-party budget apps lose data on local-only setups.

Why does a finance app need a web client when I have it on my phone?

Three concrete reasons: (1) long planning sessions — setting up category limits, reviewing yearly charts — are easier on a laptop than a phone; (2) emergency access from someone else's device when you've left your phone at home; (3) recovery when you lose or break your phone and are waiting for a replacement. Martia runs Android, iOS and web off the same database; most apps in the European market are mobile-only.

Does a subscription bought on iOS work on Android?

No. Subscriptions billed through the App Store and Google Play are two separate billing systems. If you buy Premium on an iPhone and later switch to Android, the iOS subscription stays on iOS. Your user account in the app usually keeps the premium status (if the app has its own user system), but cancelling and re-subscribing on Android is a separate transaction. Apps that bill through their own website (like YNAB) avoid this entirely.

How does PSD2 Open Banking affect cross-platform budget apps in Europe?

Under PSD2, licensed account information services (AIS) can read transactions from European banks with your consent. The consent is tied to your bank account, not your phone — so whichever device you log into the app from, you see the same transaction history. The only catch: PSD2 currently requires re-authorisation every 90 days. A new phone is a good opportunity to refresh all bank connections at once. See what Open Banking is and whether it's safe for the regulatory background.

Sources

StatCounter GlobalStats (2026), Mobile Operating System Market Share Europe, gs.statcounter.com
AppsFlyer (2025), Europe Finance App Trends — Retention Benchmarks, appsflyer.com
European Commission (2015), Directive (EU) 2015/2366 on payment services in the internal market (PSD2), eur-lex.europa.eu
Apple Developer (2026), App Store Review Guidelines, developer.apple.com
Google Play Console (2026), App release process and review timing, support.google.com

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