If you hope to build a seven-figure retirement nest egg starting from scratch in your mid-40s, you've got some heavy-duty saving ahead of you. Is it possible? Sure, theoretically. As a practical matter, though, I'd have to say that for many, if not most people in your situation, it's a long shot.
Fortunately, there's a better way for people who are getting a late start to go about preparing for retirement than shooting for a big round, but essentially arbitrary, number. I'll get to that in a minute.
For the purposes of this exercise, I'm going to assume you're 45, have nothing saved and would like to retire at 67, the age at which anyone born in 1960 or later becomes eligible for full Social Security benefits. That gives you 22 years to build your nest egg. If you start immediately, you would need to save about $1,875 a month to have $1 million at retirement, assuming a 6% annual return.
I think by most people's standards, $1,875 a month, or $22,500 a year, is a prodigious amount to devote to savings. If you earn $50,000 a year, you're talking about setting aside 45% of salary. Even if you pull down $100,000 a year, that's still 22.5% of earnings, well above what most people manage to save.
You can lower that monthly savings nut a bit by extending your time in the workforce. (You can also lower it by shooting for a higher rate of return, but I don't think that would be realistic or prudent.)
For example, if you're able to work to age 70 -- hardly a given, as many people find themselves forced to retire earlier than they'd planned) -- that gives you three more years to save, lowering the amount you'd have to put away each month by $400 to about $1,475, or $17,700 a year. That may be a bit more manageable, but I think most people would still find $1,475 a month a tough target to meet. Indeed, for many people it's beyond their reach.