A “how long will my money last calculator” estimates how many months or years your savings can support your spending before you run out of money, based on your starting balance, withdrawals, and investment returns. Many retirement- planning and savings tools online already provide this type of runway estimate in a simple, interactive way.

What this calculator usually asks for

Most “how long will my money last calculator” tools use a few core inputs to estimate your runway. Common fields include:

  • Current savings or net worth (the starting pot of money you could live on).
  • Monthly or yearly spending/withdrawals , including housing, food, insurance, and other expected costs.
  • Any ongoing income , such as part‑time work, pensions, or Social Security, which reduces how much you must withdraw from savings.
  • Assumed investment return (for invested money) and sometimes inflation , often applied on a monthly or yearly basis.

With these numbers, the calculator simulates each period: it applies growth to your investments, subtracts your withdrawals (net of other income), and counts how many periods until the balance hits zero.

Typical uses and scenarios

People most often use a “how long will my money last calculator” in a retirement or early‑retirement context. Common scenarios:

  • You stop working and want to know whether your current savings can cover your desired lifestyle until at least your life expectancy.
  • You plan a sabbatical or career break and need to estimate your “runway” (how many months/years you can live on savings).
  • You test “what‑if” changes, such as increasing expenses, lowering investment returns, or changing withdrawal amounts to see how your timeline changes.

Some calculators also include visual charts and scenario sliders so you can quickly explore different assumptions and stress‑test your plan.

How this ties to common rules of thumb

Beyond calculators, many planners use simple withdrawal rules to approximate how long money might last. A popular rule is the 4% rule , which says:

  • In the first year of retirement, withdraw about 4% of your portfolio, and then adjust that dollar amount for inflation each year.
  • Historical research suggests that with a diversified portfolio, this has often been safe for roughly a 30‑year retirement horizon, though outcomes vary with market returns and inflation.

More advanced tools run full simulations (such as Monte Carlo) to show the probability that your money lasts to a given age, rather than a single fixed year estimate.

Want to roughly estimate it yourself?

Without a formal calculator, a simple mental framework is:

  1. Estimate annual spending in retirement or during your break.
  2. Subtract any reliable annual income (pensions, Social Security, side work).
  3. Compare the net withdrawal to your savings:
    • If withdrawals are small relative to your balance and you assume some growth, money may last decades.
    • If withdrawals are large, your “runway” shrinks and you may need to adjust spending, work longer, or save more.

Online, you can find multiple “how long will my money last” and retirement longevity calculators from banks, credit unions, and independent financial sites that walk you through this step by step.

Information gathered from public forums or data available on the internet and portrayed here.