To calculate the UK capital gains tax, it is necessary to supply the following information:

• Your total capital gains for the tax year, divided into personal and entrepreneurial gains, where the entrepreneurial gains are those gains that qualify for Entrepreneurs' Relief as long as the lifetime limit has not been reached. If the tax year is split as a result of budget changes, the tool requests capital gains before and from that date.
• The tax year, noting that this runs from 6 April in the first year to 5 April in the next.
• If relevant for the tax year, your total taxable income after the deduction of any tax-free allowances and reliefs that you are entitled to.
• If you have entrepreneurial capital gains, you also need to enter your lifetime total of capital gains qualifying for Entrepreneurs' Relief that was reached before the tax year starts. Since this lifetime gains count dates from the first tax year of the new capital gains tax regime (2008-09), it should be kept at 0 for that tax year.

Note: This tool has been developed in line with the new capital gains tax regime, starting in the tax year 2008-09, so does not support calculations for previous tax years, where the taper relief and indexation allowance were relevant.

The data (e.g. rates and allowances) used by this tool was obtained primarily from...

http://www.hmrc.gov.uk/rates/cgt.htm

with the lifetime limit for Entrepreneurs' Relief obtained from...

http://www.hmrc.gov.uk/cgt/businesses/reliefs.htm#1

Associated tool link: http://www.coggit.com/tools/uk_capital_gains_tax_reckoner.html