Let's say you are 50, and despite working for 25 years, you have only socked away $500,000 of your $1 million goal. All is far from lost. If you earn a conservative 5% on those funds, without ever adding a dime to the original pile, you will have just over $1 million at age 65.

Remember, you aren't gearing up to spend your entire nest egg the day you turn 65. Most of it will keep earning money for you over your 70s and beyond. So will the fresh money that you save beginning now, at age 50.

Let's say you put away $400 a month. Say it compounds at a conservative 5% each year. You don't touch that money for 30 years — after all, in the early years of your retirement, you are living off the money you saved earlier.

That $400 a month becomes nearly $107,200 when you hit 65 and stop saving. But your nest egg still keeps compounding at 5% and is nearly $335,000 or so by the time you are 80. Yes, you are doing all of your original and catch-up saving in a tax-deferred account like a 401(k).

Here are ways to get that $400 per month, and sometimes much more:

• Downsize your home now, not after you retire. Consider moving to cheaper townhouse or condo, and pocket the monthly mortgage payment difference. Remember that you don't want to unexpectedly find that you can't afford a larger mortgage payment in retirement, so better to downsize now while you are still working.

Not ready to downsize? Renting out your basement or garage can yield a hefty monthly income.

• Stash your federal tax refund into your retirement nest egg. The average refund across all income groups for returns filed this year for 2019 was $2,778 as of May 15, according to the IRS. That's a decent chunk of your $400 a month goal.

• If you have to buy a car, make it a used one. A three-year-old automobile costs on average $14,450 less than a new one, according to Edmunds data from November 2019. Used doesn't mean clunker. The bestselling Toyota Corolla starts new this year for $19,600 and goes up to nearly $27,000, for an average $23,300, depending on the goodies, according to Edmunds. A three-year-old model from 2017 roughly costs an average $11,400.

Edmunds said that last March, the average car payment for new vehicles with a 72-month loan, the most common kind, hit a record high of $569. For used cars with an average financed price of $22,201 — close to our used Corolla above — the average monthly payment was $409. That's a difference of $160 a month right there.