A currency converter that works with no signal at all
Most converter apps are a web page in a jacket. The moment the signal goes, they show you a spinner — usually at the exact moment you needed a number.
There is a specific, recurring moment this page is about. You have landed, or you are three streets into a market, or you are at 38,000 feet looking at a duty-free catalogue. Someone has quoted you a number. Your phone has no useful data connection. And the app you installed for exactly this situation is showing you a loading indicator.
That failure is not an edge case. It is the normal state of travel.
What "works offline" actually has to mean
Almost every currency app claims offline support, and the claim covers at least three very different behaviours. Worth knowing which one you have before you rely on it:
| Behaviour | What happens with no signal |
|---|---|
| Genuinely offline-first | Rates live on the device. The app opens instantly and converts. It tells you how old the rates are, and refreshes on its own when a connection comes back. |
| Cached, but reluctant | It works, but only if you opened it recently enough. Sometimes it blocks on a network call first and you wait through a timeout. |
| Offline in the marketing only | A spinner, an error, or a stale number with no indication that it is stale — which is the worst of the three, because you act on it. |
The third category is common enough that it is worth testing your converter before a trip rather than during one. It takes ten seconds: turn on airplane mode, force-quit the app, open it, and convert something. If it hesitates, it will hesitate in the market too.
Why so many converters need a connection
Two reasons, and neither is really about exchange rates.
The first is advertising. An ad-funded app has to reach an ad network before it can show you the screen it makes money from, so the network call sits in front of the thing you actually opened the app for. The second is architecture: it is simply easier to fetch a rate on demand than to store a rate table, version it, and reason about how stale is too stale.
Both are decisions about the business, not limits of the technology. Exchange rates for travel move slowly enough that a table from this morning is fine for working out whether a taxi fare is reasonable this afternoon.
How RoamRate handles it
Rates are stored on the device and refreshed in the background whenever the phone has a connection. There is no network call between you and the number: the app opens straight into the keypad and converts immediately, in airplane mode, on a plane, in a basement, in a country where your eSIM has quietly stopped working.
It also shows you how old the rates are, because "offline" without "and here is how stale this is" is a different kind of dishonesty. If the last refresh was two hours ago, the app says two hours.
There is no account, no advertising network, and no analytics, which removes the usual reasons for an app to want the network before it will talk to you.
If all you need is a plain conversion and you are on iOS 18 or later, your iPhone already has one built into the Calculator app, free, and it works offline. We wrote an honest page about when that is genuinely enough and when it isn't — read it before you spend anything, here or elsewhere.
Converting with no phone at all
Batteries die, and the most reliable offline converter is the one in your head. For every currency worth learning we publish a cheat sheet: a single rule of thumb, how wrong that rule is, and the point at which it stops being the right rule. The method behind them takes about five minutes to learn and works for the rest of your life.
Convert with no signal, in one hand
Free for US dollars, euros, pounds, yen and Canadian dollars. One payment of $4.99 unlocks all 150+ currencies — instead of the $15 to $20 a year that most converters now charge.
Download on the App Store