First of all happy new year to you. Tax can be so complicated for ordinary people like me. Where I came from, income generated from online business such as blogging still not taxable. Unless the blog is declared as a business entity.

For offline businesses, basic calculation for taxable income is Income less related expenses to the business. So, what we can do is to spend on items that can be used both business and personal. For example such as car and health insurance. So instead for being charged for income tax, tax will be paid under corporation tax section.