Retirement Calculator

Overview

A retirement calculator answers three questions at once: how much can be saved by the target retirement age, how much principal is needed to support a given income, and how much needs to be saved each month to close any gap. The math behind all three is the same compound-interest engine, but the inputs change depending on which question is being asked. Real retirement planning also depends on Social Security or equivalent state pensions, healthcare costs, taxes, and lifestyle choices that are hard to predict decades in advance, so the result here is a useful baseline rather than a final answer.

The most cited rule of thumb in personal finance is the '4% rule.' Coined by financial planner William Bengen in 1994 and later refined in the Trinity Study, the rule says that withdrawing 4% of the starting portfolio in year one, then adjusting that dollar amount for inflation each year, has historically survived most 30-year retirements in US market history. It is not a guarantee, and Bengen himself has updated the safe withdrawal rate to closer to 3.5% in low-yield environments, but 4% remains the most common starting point. Multiplying the desired annual income by 25 gives the rough target portfolio (for example, $40,000 a year implies a $1,000,000 nest egg).

Compound interest does most of the heavy lifting. Money invested today grows not only on the original contribution but on all the interest already credited, year after year. The longer the horizon, the more dramatic the curve: an extra 10 years of saving in a 30s can outweigh an extra 10 years of saving in a 50s, even at the same percentage rate. The historical real return of a diversified US stock portfolio is roughly 6 to 7 percent after inflation, while a balanced 60/40 portfolio sits closer to 4 to 5 percent. These are averages, not promises, and sequence-of-returns risk (a bad market right after retirement) can quietly shrink a portfolio even when long-run returns are fine.

Inflation is the silent partner. At a 3% inflation rate, prices double in about 24 years, so a comfortable $50,000 lifestyle today needs roughly $100,000 a year in 24 years to feel the same. Inflation assumptions should be checked against recent CPI data from the US Bureau of Labor Statistics or the equivalent national agency. Social Security, pensions, and other guaranteed income should be subtracted from the target annual income, since they reduce what the portfolio itself has to generate.

How to use

1. Enter current age, target retirement age, and life expectancy used for planning (often 90 to 95).
2. Add current savings, monthly contribution, expected annual return, and expected inflation rate.
3. Include any guaranteed income (Social Security, pension) and the desired annual retirement income in today's dollars.
4. Submit to see projected portfolio at retirement, the safe withdrawal estimate, and the monthly savings needed to close any gap.

Formula

Interpreting your results

A 'green' projection means current savings and contributions are on track to fund the target income. A 'red' projection means the gap is too large under the current assumptions, and the calculator shows what monthly savings, retirement age, or spending target would close it. Numbers assume constant returns and constant inflation, which never happens in practice, so stress-test by rerunning the calculation with a 1 to 2 percent lower return and a 1 percent higher inflation rate. The Consumer Financial Protection Bureau (CFPB) and the Employee Benefit Research Institute (EBRI) publish benchmark replacement ratios (typically 70 to 85 percent of pre-retirement income) that are useful sanity checks against the result.

Frequently asked questions

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