It used to be that homeowners had to calculate and "roll over" profit/gain on a house to the next one they bought, and so forth until their final home. Then all those years of houses and accumulated gains came due -- with one lump sum exclusion.
Now, however, every taxpayer receives a $250,000/$500,000 per couple "exclusion from gain" on each principal residence they sell (but only one every 2 years). That means if you have lived in a home for quite a while and have seen the value go up, you have some pretty favorable tax treatment. It takes documentation --and good professional tax advice -- but it can save Downsizers and Senior movers quite a bit on taxes. We can refer you to good tax advisors as needed.