Annuity Payout Calculator — How Long Will Your Money Last?

How Annuity Payout Calculator Works

PMT = P x r / [1 - (1 + r)^-n] . n = ln[PMT / (PMT - P x r)] / ln(1 + r)

The first formula calculates the fixed periodic payment that will deplete a starting principal to exactly zero over n periods. The second formula isolates n — solving for how many periods a given fixed payment amount will last before the principal is exhausted. All math uses decimal.js for high precision, critical when computing the log-based duration formula.

PMT

Periodic Payment — The fixed withdrawal amount each period (monthly or annually). The annuity payout formula is designed so that the balance reaches exactly zero at the end of the specified term, assuming a constant rate of return.

r

Period Rate — The annual rate of return divided by the number of periods per year (divided by 12 for monthly payouts, or 1 for annual payouts).

P

Principal — The starting lump sum. The calculator models how this balance declines over time as you make regular withdrawals while earning returns on the remaining balance.

4% Rule

Safe Withdrawal Rate Benchmark — A widely cited guideline from the Trinity Study: withdrawing 4% of your portfolio in year one, then adjusting for inflation, has historically provided a 95%+ success rate over 30-year retirements. On $500,000, that is $20,000/year or approximately $1,667/month.

Source: The annuity payout formula is derived from the present value of an ordinary annuity: PV = PMT x (1 - (1+r)^-n) / r. Solving for PMT gives the payout formula; solving for n uses natural logarithms. This is the same math underlying mortgage amortization, only reversed — instead of paying off a loan, you are depleting an asset.

How to Use

1. Select "Monthly Payout" or "How Long" mode depending on what you want to calculate.
2. Enter your starting principal, expected annual rate of return, and payout frequency.
3. Review the depletion chart to compare how long your money lasts with and without investment returns.

Quick Reference

Common Uses

• •Determine how much income you can safely withdraw from a lump-sum retirement account without outliving your savings.
• •Compare different payout frequencies and investment return assumptions to find the right annuity strategy for your retirement.
• •Plan the transition from accumulation to decumulation by modeling how long your nest egg will last under various scenarios.

Understanding the Result

An annuity payout calculator answers one of the most anxiety-inducing questions in retirement planning: "Will I outlive my money?" The key insight is that your remaining balance continues to earn investment returns even as you make regular withdrawals. A $500,000 portfolio earning 5% annually can generate $2,688/month for 25 years before reaching zero — significantly more than the simple division of $500,000 divided by 300 months which only gives $1,667/month with no investment return. The difference between a 0% return and a 5% return on the same starting principal is enormous: it can add 10 or more years of payout duration. This calculator also accounts for the self-sustaining threshold — if your withdrawal rate is low enough that it does not exceed the interest earned, your principal can last indefinitely.

Worked Examples

Frequently Asked Questions

What is a realistic expected rate of return for a retirement portfolio?

The expected return depends entirely on your asset allocation. A conservative portfolio (heavy in bonds and cash): 3-4%. A balanced portfolio (60% stocks / 40% bonds): 5-6%. A growth-oriented portfolio (80%+ equities): 6-8%. The return during the payout phase matters even more than the accumulation phase return because of sequence-of-returns risk — a market downturn early in retirement can be devastating if you are simultaneously withdrawing funds. Many financial advisors recommend using a conservative 4-5% expected return for planning purposes.

What is the 4% rule and is it still valid?

The 4% rule, derived from the Trinity Study, found that withdrawing 4% of a balanced portfolio in year one and adjusting for inflation each subsequent year had a 95%+ historical success rate over 30-year retirements in US market data. Critics note that the current low interest rate environment and historically high market valuations may reduce future expected returns. Many retirement planners now suggest 3.5% to 4% as a more conservative "safe withdrawal rate," especially for those retiring before age 60.

What happens if my withdrawal exceeds my earnings?

When your periodic withdrawal exceeds the interest earned on the remaining balance, you are drawing down principal. Your balance declines each period until it eventually reaches zero. This calculator precisely models that depletion curve. If your withdrawal is less than or equal to the interest your balance earns, your principal is self-sustaining and will last indefinitely — meaning you are living entirely off the investment returns without ever touching the original principal.

What is sequence-of-returns risk and why does it matter for annuities?

Sequence-of-returns risk is the danger that poor investment returns occur early in the withdrawal phase, which disproportionately shortens portfolio longevity. Imagine two retirees, both with $500,000 earning a 6% average return over 25 years. Retiree A experiences -15% returns in years 1-2 then strong recovery; Retiree B gets the bad years later. Despite the same average return, Retiree A may run out of money years earlier because withdrawals during downturns lock in losses. This is why conservative return assumptions and flexible spending plans are critical for retirement.

Should I take the lump sum or the annuity payment from my pension?

This calculator helps answer that by showing you what monthly payout the lump sum can generate. If your employer offers a $500,000 lump sum OR $2,500/month for life: plug in $500,000 as principal, your life expectancy as years, and a conservative return (e.g., 4-5%). If the calculator shows a sustainable payout above $2,500/month, the lump sum may be more flexible and leave money for heirs. If it shows less, the guaranteed pension annuity is the better deal. Also consider: employer pension is guaranteed, while self-managed lump sum carries market risk and requires discipline.

Pro Tips

• →Use a conservative return assumption (4-5%) rather than historical averages (7-10%) — the payout phase is far more sensitive to low returns than the accumulation phase due to sequence-of-returns risk.
• →If the calculator shows your money lasts "indefinitely," you have achieved financial independence — your withdrawals are lower than your annual returns, meaning you will never drain the principal.
• →Pair this calculator with the 4% Rule: take your total savings, multiply by 0.04, divide by 12 — that is your sustainable monthly withdrawal. Compare that result against this calculator set to a 30-year duration.
• →For early retirement (before 60), use a lower withdrawal rate (3-3.5%) to account for the longer horizon — the Trinity Study was for 30 years, not 50+ years.
• →The inflation toggle is critical: a fixed $2,684/month seems fine today, but in 25 years at 3% inflation, it has only 48% of today's purchasing power. Always check the inflation-adjusted number.

Limitations to Know

• •Constant return assumption: real portfolios experience volatility. A market crash in the first 5 years of withdrawals (sequence-of-returns risk) can dramatically shorten the payout period even if the long-term average return is met.
• •The calculator models a fixed withdrawal amount — it does not support the 4% Rule style of inflation-adjusted increasing withdrawals, which is what most financial planners recommend for retirement.
• •Taxes and fees are not modeled. Required Minimum Distributions (RMDs) may force larger withdrawals than you planned. Consult the RMD Calculator for age-based mandatory withdrawals.
• •Life expectancy uncertainty: the calculator shows exactly when money runs out under given assumptions, but in reality both investment returns and your lifespan are unknown variables.

Sources

• US Securities and Exchange Commission
• Investopedia — Annuities
• Trinity Study (Cooley, Hubbard, Walz 1998)