FMDiscount Rates

Hi - Can you please explain as to when do we use after tax WACC discount rate and before tax discount rate. - Mainly confusion is between before tax and after tax? Under what circumstance do we use them ? As per my understanding we use after tax cost of capital for NPV and investment appraisals. Where we would use [ i(1-t )] where before tax rate is provided. Considering Real and Nominal rate -- (1+m)=(1+r)(1+i) Real Rate - Use only when single inflation or no inflation ( no need to inflate variables) Nominal Rate - Use when more than one inflation rate ( inflate variables) For Lease vs Buy -- use Before Tax Cost of Debt (instead of cost of capital) Please correct me if I am wrong in the above understanding. Thanks. Regards Aakash.