Bright Side Kit

MONEY GUIDE

How to Calculate Your Retirement Countdown: Step by Step

The example is age 35 to 65, $50,000 saved, and $800 a month at 7% a year with a $1,500,000 target — future value $1,381,801.67, contributed $288,000.00, growth $1,043,801.67, shortfall $118,198.33. Calculating your retirement countdown is five steps, and this guide walks through them.

The formula, in one paragraph

Your retirement countdown is the future value of your savings: what your money is worth at the age you want to retire. The months are the years between your current age and your target age, times 12. The monthly rate is the annual return divided by 12, and the future value is your savings grown by monthly compounding, plus each monthly contribution grown the same way. See the formula in the box below.

Step 1: Your ages

Start with your current age and the age you want to retire at. The example uses 35 and 65. The months are (65 minus 35) times 12, which is 360 months, or 30.00 years. The months are the compounding window: every month of the wait is a month your money grows, so a longer wait means a bigger future value. Retire at 60 instead and the wait is 300 months; start at 45 instead and it is 240 months.

Step 2: The future value

Take your savings, your monthly contribution, and your return. The example uses $50,000 saved, $800 a month, and 7% a year. The monthly rate is 7% divided by 12, which is 0.5833% a month. The future value is $1,381,801.67. Your contributions are $800 times 360, which is $288,000.00. The growth is the future value minus your savings minus your contributions: $1,381,801.67 minus $50,000 minus $288,000.00 is $1,043,801.67. Growth does most of the work: more than three quarters of the future value comes from compounding, not from your contributions. That is why starting early matters more than saving more.

Step 3: The shortfall

Compare the future value with your target nest egg. The example targets $1,500,000. The shortfall is $1,500,000 minus $1,381,801.67, which is $118,198.33. The shortfall is the gap your plan has to close: a higher monthly contribution, a later retirement age, or a smaller target. If the future value beats the target, there is no shortfall at all. With $100,000 saved instead of $50,000, the future value is $1,787,626.54, which beats the $1,500,000 target by $287,626.54.

Step 4: The monthly savings that close the gap

The formula also runs backwards. To reach $1,500,000 by age 65 you need $896.89 a month — the exact figure is $896.8862, so $896.89 a month reaches $1,500,004.66 and $896.88 reaches only $1,499,992.46. At $800 a month it takes 372.88 months instead — 31.07 years, to age 66.07, or about 373 months. To reach $1,000,000 by age 65 you need $487.04 a month — the exact figure is $487.0404, and at $487.04 the future value is $999,999.55. A cent less than $896.89 misses the $1,500,000 mark by a few dollars, which is why the exact figure matters.

Step 5: Coast FI

Coast FI is the age your savings alone reach your target, with no more contributions. At 7% a year, $50,000 saved now reaches $1,500,000 in 584.76 months (48.73 years), at age 83.73. That uses monthly compounding — the monthly rate is 7% divided by 12, not the annual 1.07 figure. Coast FI is the point where you can stop saving and still retire on schedule, if you are willing to wait that long. At 83.73 it is a long wait, which is why coasting alone is not a plan for retiring at 65.

What NOT to do

Do not judge by the future value alone: $1,381,801.67 at 65 is a plan, not a promise, and the return is the lever you control least. At a 5% return instead of 7%, the future value is $889,194.12, not $1,381,801.67. Do not trust a 0% return: with no return at all the future value is $338,000.00, just what you put in, with $0.00 of growth. Do not start late without counting the cost: starting at 45 instead of 35 gives $618,678.27, not $1,381,801.67, a loss of $763,123.40. Do not use a target age at or before your current age: the calculator asks for a target age after your current age.

Future value = savings × (1 + monthly rate)months + monthly × ((1 + monthly rate)months − 1) ÷ monthly rate; months = (target age − current age) × 12; monthly rate = annual return ÷ 12; total contributed = monthly × months; growth = future value − savings − contributed; shortfall = target − future value

That box is the whole formula.

Worked example: 35 to 65 at 7%

Step 1: 35 to 65 is 360 months (30.00 years).
Step 2: future value $1,381,801.67, contributed $288,000.00, growth $1,043,801.67.
Step 3: shortfall $118,198.33 against the $1,500,000 target.
Step 4: monthly savings of $896.89 (exact $896.8862) reach $1,500,000 by 65.
Step 5: Coast FI age 83.73.

Answer: savings of $1,381,801.67 by age 65, $118,198.33 short of $1,500,000.

Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

Cite this guideBright Side Kit. “How to Calculate Your Retirement Countdown: Step by Step.” Method: months = (target age − current age) × 12; monthly rate = annual return ÷ 12; future value = savings × (1 + monthly rate)months + monthly × ((1 + monthly rate)months − 1) ÷ monthly rate; contributed = monthly × months (monthly savings only); growth = future value − savings − contributed; shortfall = target − future value. Example: age 35 → 65, $50,000 / $800/mo / 7% / $1,500,000 → 360 months, 30.00 years, future value $1,381,801.67, contributed $288,000.00, growth $1,043,801.67, shortfall $118,198.33. Bright Side Kit. "How to Calculate Your Retirement Countdown: Step by Step." https://brightoolbox.com/guides/how-to-calculate-retirement-countdown/ Accessed October 25, 2026.
Planning estimate, not professional advice: check the return, the savings, and the target with your own numbers before you rely on them.

Frequently asked questions

How do I calculate my retirement countdown?

Work out the future value of your savings at your target retirement age. The months are (target age minus current age) times 12, the monthly rate is the annual return divided by 12, and the future value is your savings grown by monthly compounding plus each monthly contribution grown the same way. At 35 to 65 with $50,000 saved and $800 a month at 7%, the future value is $1,381,801.67.

How much will I have if I save $800 a month for 30 years?

$1,381,801.67 at 7% a year. With $50,000 saved already and $800 a month from age 35 to 65, your savings are worth $1,381,801.67 at 65. You contribute $288,000.00 and growth adds $1,043,801.67. That is $118,198.33 short of a $1,500,000 target.

How much do I need to save a month to reach $1.5 million by 65?

$896.89 a month. The exact figure is $896.8862, so $896.89 a month reaches $1,500,004.66 by 65 and $896.88 reaches only $1,499,992.46. At $800 a month it takes 372.88 months instead — 31.07 years, to age 66.07.

What is Coast FI?

The age your savings alone reach your target, with no more contributions. With $50,000 saved at 7% a year, your savings alone reach $1,500,000 in 584.76 months (48.73 years), at age 83.73. Coast FI is the point where you can stop saving and still retire on schedule, if you are willing to wait that long.

What happens if I start saving at 45 instead of 35?

Your savings reach $618,678.27 instead of $1,381,801.67. Ten fewer years of compounding cost $763,123.40, even though you contribute only $96,000.00 less. Starting early is worth more than saving more, because the early money compounds for the whole 30 years.

Related calculators

Money CalculatorsEvery money calculator on the site. Retirement Countdown CalculatorYour retirement countdown, worked out. FIRE CalculatorYour FIRE number and years to FI, worked out. Retirement Savings CalculatorYour retirement savings, projected. Retirement Number CalculatorHow much you need to retire, worked out. Savings Rate to Retirement ChartHow your savings rate sets your retirement age.