Move the sliders and watch the score change in real time. This is exactly why the variables in your plan matter so much more than the number itself.
The S&P 500 returned -0.95% annually from 2000 to 2009. An entire decade. Negative. Adjust your return assumption to 3% and see what happens.
From 1965 to 1982 inflation averaged above 6% for seventeen straight years. Try moving your annual inflation rate to 6% and see what happens.
Two minutes. Plain English. No sales pitch.