Literally have met no one who regretted retiring early in any circumstance; and can not find these mythical humans. And that is an issue with the public at large thinking they need more to retire on, than they really do. Many think they need at least $1.5M for each person in the bank, plus other things like paid off house and maybe a small pension, and insurance coverage. Its just not true.
Start with determining what you need per year to live on, including various insurance premiums (cause you need those too). then figure the retirement requirement from that.
But.... Do understand that there are many who say they want to retire and they have nothing at all. They have no SS benefit cause they never worked reportable income for SS (family worked, not them; or special job like old government jobs that had no SS). Or they have nothing I savings at all. or they have big debts due to nasty medical situations.