A taximeter calculates a fare from two things: the distance travelled and the time the journey takes. It starts with a fixed opening charge, then adds amounts as the vehicle covers ground or sits in slow traffic, switching between the two depending on whether the cab is moving fast enough. The rate it applies comes from a tariff set by the local licensing authority, not by the driver.
What the meter is actually measuring
The meter is a sealed, calibrated device wired into the vehicle. It reads distance from the cab's movement and time from its own clock, then converts both into money using preset tariff rates. A "tariff" here simply means the schedule of charges that applies to a given journey.
At any moment the meter is charging on one of two bases. When the cab is moving above a set speed, it charges by distance — a small increment every fraction of a mile. When the cab slows below that speed or stops, it switches to charging by time instead, so a fare keeps rising even when the wheels are still.
This switching is why two journeys of the same distance can cost different amounts. A clear run charges mostly on distance; a crawl through congestion charges more on waiting time. The meter handles the changeover automatically, so the displayed figure reflects whichever measure is currently ticking.
The flag-fall, the distance run and waiting time
A taximeter calculates a fare from two things: the distance travelled and the time the journey takes.
The "flag-fall" is the initial charge shown the moment the meter is started. The name dates from older meters that had a physical flag the driver lowered to begin a fare. It covers a set minimum distance or time, after which the per-unit charges begin.
After the flag-fall, the fare builds in small steps. Each step typically covers a short distance, such as a fraction of a mile, or a short period of waiting time. The meter rounds up to the next step, which is why you sometimes see the figure jump just as you arrive.
Waiting time covers any period the cab is stationary or moving very slowly — at traffic lights, in a queue, or if you ask the driver to wait. The relevant elements of a metered fare are usually:
- Flag-fall — the fixed opening charge that starts the meter.
- Distance charge — added in increments once the cab is moving above the switch-over speed.
- Waiting-time charge — added in increments when the cab is slow or stopped.
- Surcharges — extra fixed amounts permitted in certain circumstances, added on top.
These rules apply to licensed hackney carriages — the cabs you can flag down or pick up at a rank. Private hire vehicles, which must be booked in advance, are not always required to run a meter, though many do; their pricing can be agreed at the time of booking instead.
Why tariffs change with the time of day
Most authorities set more than one tariff, and the meter applies whichever fits the time and date. A common arrangement is a standard daytime rate, a higher evening or night rate, and a higher rate again for Sundays and public holidays. The driver selects, or the meter automatically applies, the correct tariff for the moment the journey begins.
The reasoning is straightforward. Demand and operating conditions vary across the week, and night and holiday work is less convenient to cover, so the agreed rates reflect that. The tariff numbers are usually displayed inside the vehicle, often on a card or sticker, so you can check which one is running.
If a journey crosses from one tariff period into another — for example, starting just before a night rate begins — the meter generally stays on the tariff that was in force when it was started, unless the local rules say otherwise. It is reasonable to ask the driver which tariff is set if the displayed number is unclear.
Surcharges you might see added
A surcharge is an extra fixed amount added to the metered fare in specific situations that the local tariff permits. It is not part of the running distance or time charge; it appears as an addition at the end or is keyed in by the driver. Common examples include charges for extra passengers above a stated number, for bulky luggage, or for journeys at particular times such as late at night or over the festive period.
Some areas allow a soiling charge if a passenger leaves a mess that takes the vehicle out of service. Bookings made by phone or app may carry a booking fee, depending on the operator. What is and isn't allowed depends entirely on the local rules, and any surcharge should correspond to something the authority has authorised.
If a surcharge appears that you don't understand, you can ask the driver to explain it and to point to where it is listed. Authorised charges are typically set out on the tariff card displayed in the vehicle.
Who actually sets the rates
For hackney carriages, the maximum fares are set by the local licensing authority — usually the council for the district where the vehicle is licensed. The council decides the flag-fall, the distance and time rates, the tariff bands and the permitted surcharges. Meters are then calibrated and sealed to match those figures, and are checked periodically.
The figure on the meter is a maximum, not necessarily a fixed price. A driver can charge less than the meter shows but should not charge more for a journey within the licensed area. Journeys that run outside that area may be subject to a fare agreed beforehand, since the council's set tariff does not apply beyond its boundary.
Because each authority sets its own tariff, fares for the same distance can differ between neighbouring areas. If you want to know the rates that apply where you are, the licensing authority publishes its current tariff, and the card inside a licensed cab should match it. Checking the displayed tariff before setting off is the simplest way to know how the fare will add up.