Policy guide has very a good illustration.
http://www.ukba.homeoffice.gov.uk/sitec ... olicy1.pdf
42. For example, the Tier 1 Migrant has been in the UK for 6 months and is making an application at the same time as his/her spouse and two children. He/she must show that he/she has £1600 for his spouse and a further £1600 for each child, in addition to £800 required for his/her own support. In total the family will require evidence that they hold £5600 in available funds (£1600 x 3 = £4800 + £800).
43. If the same Tier 1 Migrant and his family had been present in the UK for two years, they would require evidence that they held £2399 (£533 x 3 = £1599 + £800) in available funds.
44 .If a family member applies separately from the Tier 1 Migrant, there must still be enough funds to support each member of the family. Therefore in the example above, if the family has a third child, the main applicant has been in the United Kingdom for two years and the family applies for leave to remain for the third child