Double-check the age gap, current savings, monthly contribution, expected annual return, contribution timing, and 4% income assumption before relying on a retirement savings projection.
The Retirement Calculator derives the saving horizon from your current and target retirement ages. It then shows a projected nest egg, estimated monthly retirement income under the 4% rule, and total contributed. The tool runs locally in your browser, so the numbers you enter are not uploaded, but the accuracy of the illustration still depends on the inputs and assumptions you supply.
Begin with an input audit, not the final balance
Start with the two ages. The projection uses the difference between them to calculate the number of months until retirement: n = (retirement age − current age) × 12. The retirement age must exceed the current age. An age entered in the wrong direction, or a mistaken birth year used to derive the age, can change the entire saving horizon.
Next, distinguish the three cash-flow inputs. Current savings is the starting lump sum, the monthly contribution is a level deposit made at the end of each month, and the expected annual return is the percentage used for monthly compounding. For example, enter 7 for a 7% expected return. The implementation converts that annual percentage to a monthly rate by dividing it by 100 and then by 12.
Check the validity of every figure. Negative ages, savings, contributions, and returns are rejected. At a zero return, the contribution term reduces to monthly contribution × n. Because the calculation has no separate fields for taxes, fees, inflation, or changing contribution amounts, do not assume that any of those factors are already reflected in the output.
Run the retirement projection in the right order
Use the calculator in this sequence so that each output can be checked against the input that produced it:
- Enter your current age and target retirement age. Confirm that the target age is later than the current age and note the resulting number of months.
- Enter current savings and the monthly contribution. Make sure both are amounts you intend to include and that the contribution is expressed as a monthly amount.
- Enter the expected annual return. Use an annual percentage, such as 7 for 7%, rather than mixing it with a monthly rate.
- Read all three outputs together. These are the projected nest egg at retirement, estimated monthly retirement income using the 4% rule, and total personally contributed.
- Repeat the calculation after changing one assumption at a time. Inputs update the projection immediately, so keeping a record of each set makes it easier to see which decision caused the change.
Reconcile the three outputs against their definitions
The outputs answer different questions and should not be substituted for one another. Use this reference to check each number:
| Output | Exact definition | What to verify |
|---|---|---|
| Projected nest egg | current savings × (1 + r)^n + monthly contribution × ((1 + r)^n − 1) ÷ r | Both the starting balance and contribution growth are included, using the correct monthly rate and horizon. |
| Estimated monthly retirement income | nest egg × 0.04 ÷ 12 | The result follows a fixed 4% guideline and is not tax-adjusted. |
| Total contributed | current savings + monthly contribution × n | The arithmetic reconciles to the starting savings plus every monthly deposit in the selected horizon. |
Total contributed is not another name for the projected nest egg. It records the money entered without modeled investment growth. With a positive return and a positive balance or contribution, the projected nest egg should exceed total contributed; at a 0% return, the two amounts should align. The income output is then a separate calculation based on the nest egg, so it should never be added to the nest egg as though both represented spendable account balances.
Audit the future-value math with one controlled example
The nest-egg calculation has two parts. Existing savings is compounded as a future value, while monthly contributions are treated as an ordinary annuity because each deposit arrives at month-end. For more background on that method, see future value. The product-specific future-value and 4% formula walkthrough also explains how the two components fit together.
For one control case, suppose the current age is 30, the target retirement age is 65, current savings are $50,000, the monthly contribution is $500, and the expected annual return is 7%. The monthly rate is r = 0.07 ÷ 12, and the horizon is n = (65 − 30) × 12 = 420 months.
Substituting those values gives:
Nest egg = $50,000 × (1 + 0.07/12)^420 + $500 × (((1 + 0.07/12)^420 − 1) ÷ (0.07/12)) ≈ $1,475,835.
The contribution check is $50,000 + ($500 × 420) = $260,000. The 4% monthly estimate is $1,475,835 × 0.04 ÷ 12 ≈ $4,919, or about $4,900 when rounded. This matches the rounded retirement projection and demonstrates why a result should not be judged by the nest egg alone: the income figure must also reconcile to that balance.
Keep the 4% estimate separate from guaranteed income
The 4% rule associated with the Trinity study suggests withdrawing about 4% of a retirement nest egg in the first year, adjusting for inflation thereafter, with a strong historical chance of lasting roughly 30 years. The calculator converts that annual guideline into a monthly figure using nest egg × 0.04 ÷ 12 and presents it as a ballpark amount in today’s terms.
This is a planning guideline, not a promise. Actual sustainable withdrawals can change with market returns, inflation, fees, taxes, and the length of retirement. The calculator applies 4% as a fixed guideline rather than simulating a dynamic withdrawal strategy. Its projection also makes no tax, fee, or inflation adjustment, so the displayed monthly amount should not be treated as a guaranteed or fully tax-adjusted retirement paycheck.
Check omissions before trying alternative assumptions
The projection assumes a constant expected annual return compounded monthly, level contributions made at each month-end, and no adjustment for taxes, fees, or inflation. It does not simulate changing investment returns or changing withdrawal amounts. Those limitations matter because a realistic retirement path may involve conditions the fixed model does not capture.
Use the instant recalculation to examine individual assumptions without changing several at once:
- Move the retirement age later. A later target increases the saving horizon, but it must remain greater than the current age.
- Change the monthly contribution. Confirm that the revised total-contributed figure reflects the new deposit and the same number of months.
- Use a lower expected return. The projected nest egg and the income calculated from it should move downward; obtain the exact figures from the tool.
- Return to the original inputs. Reproducing the earlier result confirms that the inputs were recorded consistently.
Returns are never guaranteed, so even a mathematically consistent projection remains an illustration rather than a forecast. The figures are estimates for general information and are not financial advice.
Complete a final retirement projection review
Before using the result in a broader retirement plan, run through this final checklist:
- Verify that the target retirement age exceeds the current age and that the month horizon is correct.
- Confirm that savings, contribution, and return are in the intended units.
- Reconcile total contributed with current savings plus monthly deposits multiplied by the number of months.
- Check that the nest-egg calculation uses monthly compounding and end-of-month deposits.
- Recalculate the monthly income as 4% of the nest egg divided by 12, while remembering its limitations.
- Review the excluded assumptions and verify important figures with a licensed financial professional.
A useful retirement projection makes its assumptions visible and reproducible, not merely favorable. If an output still does not reconcile, troubleshoot the retirement projection result before changing the target or assuming a different return.