Saving for retirement can't be done at the last minute; it takes decades of consistent effort to save hundreds of thousands of dollars. When you start early, you still have compound interest on your side. But the longer you wait to begin stashing money in your retirement account, the more you'll need to save each month.

If you've reached your 40s with nothing in your retirement fund, it will be more challenging to retire comfortably. But it can be done if you follow these three steps.

Man sitting and looking out a window

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1. Set a savings goal

The first step is figuring out how much you need to save and exactly how you'll get there. 

When determining your goal, first think about your retirement expectations. At what age do you plan to retire? How many years do you think you'll spend in retirement? How much do you expect to spend each year once you retire?

Really think about the answers, because they will significantly affect how much you'll need to save; if your estimates are off, you risk running out of money. For instance, if you assume you'll spend 15 years in retirement but you live for another 10 years on top of that, you may end up running out of savings roughly halfway into retirement. 

You can't predict exactly how long you'll live or how much you'll spend each year. But instead of winging it and hoping for the best, try to be as educated and accurate as possible when coming up with an estimate.

Next, think about any other sources of income you will have in retirement -- like Social Security benefits or a pension. You can get an estimate of how much you can expect to receive from Social Security by creating a mySocialSecurity account to give you an idea of what your future benefit amount will look like based on your real earnings. That will help you figure out how much you'll need to save on your own. For example, if you estimate you'll spend $50,000 per year in retirement and expect to receive $20,000 per year in benefits, that means the other $30,000 per year will need to come from your savings.

Finally, run your numbers through a retirement calculator to see how much you'll need to save by retirement age and what to save each month to reach that goal. Create a savings plan, and if you have access to a 401(k) that offers matching employer contributions, factor that into your plan so you know how much must come from you. Then, start socking money away.

2. Adjust your budget to save more

When you know how much you should be contributing to your retirement fund each month, you may need some budget adjustments to find the extra cash to save. Depending on just how much you must save each month, this step could be easy or nearly impossible.

If you need to be saving several hundred dollars per month (or more), it can be tempting to throw in the towel and assume you'll never be able to. But it's easier than you may think to find extra cash in your budget.

First, start tracking your expenses; it can be easy to overspend when you're not watching where all your money is going. The average U.S. household spends close to $500 per month on unnecessary expenses, according to a survey from Charles Schwab, even though approximately 60% of those survey participants said they're living paycheck to paycheck. Once all your expenditures are laid out in front of you, it's easier to see where you're spending too much.

Making small cuts across several categories in your budget can potentially help save hundreds of dollars per month, but if that's not enough to reach your goal, you'll need more-drastic changes -- like downsizing your home or selling your car. These are big decisions, but they could help you save a lot more for retirement.

3. Consider tweaking your retirement plans

If you can't save enough to reach your goals, you might need to readjust your retirement expectations. That may involve working a few years longer than you anticipated so you have more time to save, or scaling back your retirement expenses.

Another option is to delay claiming Social Security benefits to earn bigger checks. You'll receive your full benefit amount at your full retirement age (FRA), which is either 66, 66 plus a few months, or 67. If you wait until after your FRA to begin claiming, you'll receive extra money each month -- up to 32% more on top of your full amount if you have a FRA of 66 and you wait to claim until age 70.

Delaying Social Security or working longer may not be ideal, but you'll need to make sacrifices at some point. If you're not willing to adjust your retirement expectations, you'll need to make more sacrifices now so you can boost your savings. So think about your options and consider your priorities. Would you rather live a more comfortable lifestyle now and make cuts in retirement? Or would you prefer to save more now and enjoy a more financially stable retirement?

Saving for retirement is never easy, and can be particularly difficult if you're in your 40s with little to nothing saved. But that doesn't mean it's impossible. If you're willing to make some financial sacrifices, you can still enjoy a comfortable retirement even if you're off to a late start at saving.