Is the property you are planning to sell your main home? If it is and it has been your only or main home since you bought it, then you won't have to pay Capital Gains Tax on any gain you make as it will be covered by the principle private residence exemption which you can read about here
The amount of CGT payable is affected by the level of an individual's other income as you thought. There are two rates of CGT, 18% and 28%. The rate or combination of rates that an individual will pay will be dependent on the level of their income and the net taxable gain in the tax year that the property or other asset is disposed of. The first £11,000 of gains made in 2015/16 will be tax free. If a again occurs in 2015/16, one of the following scenarios will apply:
1 If the sum of other income and the net taxable gain is £42,385 or less in 2015/16, then all the taxable gain will be charged to CGT at 18%.
2 If other income alone is £42,385 or more in 2015/16, then all the taxable gain will be charged to CGT at 28%.
3 If other income alone is less than £42,385 in 2015/16 but greater than £42,385 when the net taxable gain is added, then part of the net taxable gain will be charged to CGT at 18% and part at 28%.
I hope this helps but let me know if you have any further questions.