Does NFC work when your phone is switched off?
Reading a tag, no: that needs the phone to generate a field, which needs it running. Paying can be a different matter, because some devices reserve a little power for a payment credential after the phone shuts down. Which devices, and for how long, is a manufacturer question.
Reading needs power
When a phone reads a tag it is the active side: it generates the field that powers the tag and it issues the commands.
That takes energy and takes software. A phone that is off does neither, so it reads nothing.
This is the opposite of the tag's situation, where being unpowered is the normal state and the reader supplies everything.
Paying can be different
When a phone pays, it is behaving like a card, and a card works with no power of its own because the terminal supplies the field.
Some devices keep a small reserve so that a payment credential remains available for a period after the phone appears to shut down, typically when the battery is exhausted rather than when it is switched off deliberately.
Which devices do this, under what conditions and for how long, is set by the manufacturer and the platform and changes between generations. The device documentation is the authority.
The two behaviours are frequently conflated, and the resulting belief is that a phone that is off can still read tags. It cannot.
Off is not the same as locked
Most questions phrased as when the phone is off are actually about the screen being off or the phone being locked, which are different states with different answers.
Both platforms behave in ways worth understanding there, and each has its own guide on the smartphone side of the site.
A phone that is genuinely powered down is the simple case: nothing happens, in either direction, except possibly the payment reserve above.
What to expect
A tag will not read against a dead phone, so a routine that depends on tapping is unavailable exactly when the battery has run out.
A travel or access credential on a phone may or may not survive the battery running out, and finding out at a barrier is the wrong moment.
Carry the physical card as a fallback where being refused entry matters, which is the practical conclusion regardless of which device you have.
And test it yourself rather than relying on a general answer, since this is one of the few behaviours that genuinely varies by device.
Frequently asked questions
Can my phone read a tag when it is off?
No. Reading requires the phone to generate the field and run software, and a phone that is off does neither.
Why can it still pay then?
Paying is the reverse role, where the terminal supplies the field. Some devices keep a small reserve for it.
Does that work on every phone?
No. It depends on the manufacturer, the platform and the generation, and the device documentation is the authority.
What should I do about a travel pass?
Carry the physical card where being refused entry matters, and test the behaviour on your own device beforehand.