The calculator only takes a few seconds and is worth visiting on an ongoing basis as events change in your life.
Begin by going to Morningstar's home page. Scroll down to find:
Click as indicated. You come to:
The study is by Ibbotson Associates, well-known academic researchers in the field, and, as mentioned above the write-up at the link, explains some of their underlying assumptions. The link also includes a useful table as a guide to how much you should have save at various ages and income levels.
The results should be viewed as a guide and adapted to individual circumstances fitting the overall financial plan.
I put in 45 for the age, $100,000 for income, and $200,000 for retirement savings. The calculator found that with these inputs the saving rate should be approximately18% to replace 80% of income in retirement.