When it comes to financial goals, aiming for a nice round number — like $1 million in retirement savings — can be a powerful motivator.

While the amount you'll actually need for retirement depends on your lifestyle, income and personal circumstances, including where you live, $1 million remains a popular benchmark for retirement savings.

Reaching this goal depends not only on when you start saving, but on how much of your income you save each year.

While saving at least 10% of your income for retirement is commonly recommended by financial planners — especially for low earners — certified financial planner David Blanchett recently told CNBC that aiming for "a total savings rate of 15% is probably the right place to start."

With a 15% savings rate, even those earning well below the U.S. median income of $80,610 can still build up $1 million in retirement savings by age 65. That said, the earlier you start, the easier it is to reach this goal.

How much you need to earn to save $1 million for retirement

The following data highlights the annual salary needed to save $1 million for retirement, assuming a retirement age of 65, a consistent 15% savings rate and varying rates of return, according to CNBC calculations.

If you start at age 25:

• 4% return: $67,684
• 6% return: $40,171
• 8% return: $22,916

If you start at age 30:

• 4% return: $87,553
• 6% return: $56,152
• 8% return: $34,875

If you start at age 35:

• 4% return: $115,266
• 6% return: $79,640
• 8% return: $53,678

If you start at age 40:

• 4% return: $165,886
• 6% return: $124,783
• 8% return: $92,310

It's worth noting that many savers contribute less early in their careers when their earnings are lower, then catch up later as their income rises.

However, these figures highlight the advantage of starting early, as compound interest can lead to exponential growth the longer your money is invested. Waiting until your 40s to begin saving requires either a significantly higher salary or higher rate of return to reach the same $1 million goal.

How to know if you're on track for retirement

If you're not sure whether your retirement savings are where they need to be, widely used benchmarks from Fidelity can help you gauge your progress. While these age-based milestones offer a helpful rule of thumb, your exact savings target may vary based on your lifestyle and financial goals.

• By age 30: Have the equivalent of your annual salary saved
• By age 35: Have twice your annual salary saved
• By age 40: Have three times your annual salary saved
• By age 45: Have four times your annual salary saved
• By age 50: Have six times your annual salary saved
• By age 55: Have seven times your annual salary saved
• By age 60: Have eight times your annual salary saved
• By age 67: Have 10 times your annual salary saved

If you're unsure where you stand, CNBC Make It's retirement calculator can help estimate how much you should save based on your current age, income and existing savings.

It's also worth remembering that due to compound interest, starting with whatever you can afford — even if it's less than 10% — is better than not saving at all.

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