It takes18 years for Rahu- Ketu to complete their travel along the full zodiac signs and they stay for 18 months in each House in the Horoscope. That is they stay in the house of Aries or Mesham for a year and a half and then transits to the house of Taurus or Rishabha at the end of this period and then moves on to the next house and so on.
The transit from one house to the other becomes very significant in that the house position of Rahu-Ketu will vary for individuals thus affecting the area that they rules.
Click on the year you are interested in to find the Rahu-Ketu Peyarchi or transit details for that particular year. You can find out the dates when Rahu-Ketu Peyarchi takes place and the houses involved in the same for the year.