We are calculating the combined future value of your current assets as they compound (call it “Old Money” - and we’re calculating what the future contributions will accumulate to between now and a retirement date (call this “New Money).
The total “old” and “new” money will give you an estimate of a retirement “nest egg” at retirement. A safe amount to spend in retirement is roughly 6% of the projected account balance. 6% on $100,000 is $6,000 per year or $500 a month. Added to social security, the total should approach what you currently spend. In retirement, a 50/50 mix of stocks and bonds should earn about 7% on average. Spending 6% leaves 1% left to grow the account and protect against inflation.
Check it out. If not satisfied with the number, consider increasing the “New Money” amount by saving more (or by planning to spending less in retirement).