Identify the gap between current savings trajectory and retirement goals with catch-up contribution recommendations.
Every retirement shortfall has a price tag: the extra monthly contribution that would close it by the time you retire. This tool computes that price. You provide age, planned retirement age, current balance, monthly contributions, expected return, and a target balance; the tool projects the balance you will actually reach, reports the gap, and states the catch-up contribution needed each month to hit the target on schedule. The input most people get wrong is the expected return: one percentage point either way shifts the outcome by hundreds of dollars a month, so the projection is only as good as that assumption.
A concrete input and expected output from the current implementation.
Input
Age 40, retiring at 65. Current balance: $100,000. Saves $500 per month. Expected return: 6% per year, compounded monthly. Target: $1,000,000 at 65.
Expected output
Projected balance at 65: about $775,700. Gap vs target: about $224,300. Required contribution: about $824 per month (currently $500), a catch-up of about $324 per month.
At 6% compounded monthly for 25 years, the $100,000 grows to about $429,000 and the $500 monthly contributions to about $346,000, totaling about $776,000. Closing the remaining $224,000 gap requires about $824 per month instead of $500. Every figure follows from standard future-value arithmetic on the stated 6% assumption; a different assumed return changes them all.
The projection is ordinary compound-interest math. Your current balance is grown from today to your retirement age at the assumed annual return, and your periodic contributions are grown as a separate series of deposits; the two are added. Because returns compound for decades, small input changes become large differences, and the assumed return matters more than any other input in the model.
The projected balance is subtracted from your target to get the shortfall in retirement-year dollars. The tool then reverses the growth formula: it finds the contribution level whose own projected growth equals that shortfall by retirement. That level, usually shown as a monthly amount and as the increase over your current contribution, is the catch-up recommendation.
It can happen, especially when starting late or near retirement. IRS limits on 401(k) and IRA contributions, including the higher catch-up allowances for savers 50 and over, are set each year and can sit below what the raw math suggests. The tool's number is a savings target, not a compliance check; if it exceeds the legal limit, the realistic options are taxable brokerage savings, a later retirement date, or a lower goal.
Only what you enter. If there are fields for a match, use them; otherwise include the match as part of your monthly contribution. Social Security and pensions are income streams, not balances, and balance-target models generally ignore them. For people with substantial Social Security or pension income, that makes the gap conservative, showing a larger shortfall than reality.
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