* For simplicity assumes the most common situation - that the husband is age 75+ and has the higher income.
**National Insurance is not payable by those under 16, or over 65 (men) or 60 (women). The details are complex, but most people who do pay NI will fall into one of the categories listed, and the purpose of this is to at least give a ballpark idea of the total tax and NI liability that you face. If you wish to find out if you are Contracted In or Out, ask whoever prepares the wages, or your Personnel Department.
Tax credits NOT included. Add too much complexity to data entry.