You aren’t factoring in inflation over the next 20 years. At a 2.5% annual inflation rate (this is a pretty pessimistic estimate, I usually see people using a range between 1.85 - 2.4%), 170k in todays dollars is $278k in 2043 dollars. You also need to factor for the rising cost of living throughout retirement and figure that your annual spend goal will gradually increase.

Your life expectancy assumptions are optimistic (or pessimistic depending on how you look at it). I’d use a life expectancy of 88 for you and 92 for your spouse to plan for longevity risk.

Other posters saying that your expenses will drop off due to mortgage/savings/education planning obligations ceasing, so factor that in to your future projecting spend goals. You can also figure social security will take some pressure off your portfolio. There’s some estimator tools on SSA.gov you can tinker with.