How to Use the Retirement Calculator. The above calculator takes into account your current retirement savings plus additional contributions from your income as well as (optional) projected wage gains and evaluates your goals. It then charts your post retirement income to see if you are on track to meet those goals.. The calculator has 11 inputs, 6 of them are required: Your Current age. Annual contribution toward retirement. and/or Current retirement savings. ROI for retirement savings. You want to retire at what age. Retirement income lasts until age. ROI during retirement. There are 5 optional inputs. "/>Retirement calculator uk