Why does this not ask for my registration?

Because it does not need one. A zone camera is matched against the Euro standard held on the vehicle record, and the standard a car had to meet is settled by its fuel and the year it was first registered. Asking for a plate would collect an identifier with no use.

Is a year enough to be sure?

Almost always, but not at a boundary. Euro 6 became compulsory for new car registrations on 1 September 2015, so a diesel registered in 2015 could be either side of it. Where a year straddles a boundary the answer says so rather than picking one.

What standard does a car have to meet?

Euro 4 for a petrol car and Euro 6 for a diesel, in every UK zone that charges cars. In practice that means a petrol car registered new after 2005 and a diesel registered new after September 2015, which is the rule of thumb Transport for London publishes.

Does an electric car pay anything?

Not in an emissions zone. A battery electric car has no tailpipe, so there is no standard for it to fail. The London Congestion Charge is different: it is a charge for entering the zone rather than for what the vehicle emits, and the discount for electric vehicles has ended.

Clean air zones

ULEZ checker

Pick the fuel and the year it was first registered. No registration number needed.

What does this guide cover? Two questions settle it: what the car burns, and the year it was first registered. Those decide the Euro standard it had to meet when new, and every UK charging zone reads its verdict off that standard. No registration number is needed for any of it.

£12.50

London ULEZ, car, a day

Transport for London, Ultra Low Emission Zone (as of 8 April 2019)

Euro 4

Petrol pass mark

Transport for London, Ultra Low Emission Zone (as of 8 April 2019)

Euro 6

Diesel pass mark

Transport for London, Ultra Low Emission Zone (as of 8 April 2019)

What the checker covers

All 15 UK charging, low emission and congestion zones, each with its own verdict rather than a single national answer.
The Euro standard a car of that fuel and year had to meet when it was registered new, taken from the legislation rather than from a rule of thumb.
The Scottish low emission zones, where there is no charge to pay: a non compliant vehicle is not allowed in and the first camera capture is a penalty.
The zones that never charge cars at all, so you can stop worrying about them.

Common questions

Why does this not ask for my registration?: Because it does not need one. A zone camera is matched against the Euro standard held on the vehicle record, and the standard a car had to meet is settled by its fuel and the year it was first registered. Asking for a plate would collect an identifier with no use.
Is a year enough to be sure?: Almost always, but not at a boundary. Euro 6 became compulsory for new car registrations on 1 September 2015, so a diesel registered in 2015 could be either side of it. Where a year straddles a boundary the answer says so rather than picking one.
What standard does a car have to meet?: Euro 4 for a petrol car and Euro 6 for a diesel, in every UK zone that charges cars. In practice that means a petrol car registered new after 2005 and a diesel registered new after September 2015, which is the rule of thumb Transport for London publishes.
Does an electric car pay anything?: Not in an emissions zone. A battery electric car has no tailpipe, so there is no standard for it to fail. The London Congestion Charge is different: it is a charge for entering the zone rather than for what the vehicle emits, and the discount for electric vehicles has ended.

Sources

Each result page carries the sources for every zone it names.