The Underground received around £2.669 billion in fares for the years 2016/17. The London Underground uses for London Transport's Zonal fare system to calculate service fares.
The Underground has nine Zones, Zone 1 is the central Zone, where all sights and the hotels are located, it also consists of the loop of the Circle line along with a few stations on the south of River Thames. In Zone 6, Heathrow Airport is located, while the furthest Zone out nine is - Zone 9.
The fares vary depending on which Zone you are using. The Underground has different fares for a single journey ticket passengers, which differentiates adults and children ticket fares. Besides, there are different costs for Oyster or other contactless payment cardholders.
Under the Transport for London Byelaws and the Regulation of Railways Act (1889), those passengers who are traveling without a valid ticket will be demanded to pay a penalty fare of £80. However, if the fare is paid in 21 days period, the passenger will pay £40 instead of £80.
However, children under 11 years can travel free via the London Underground.