how long will (IT)(savings) last

The calculator runs a monthly simulation: your balance earns your expected return, gains your monthly contribution, and loses your monthly spending. It repeats that step until the balance reaches zero — or, if contributions plus growth cover your spending forever, it reports an infinite runway.

This is the right shape for questions like "how long could my savings last if I stopped working?", "how much longer do I have with my current spending?", or "how big of an emergency fund do I actually have?". For long-horizon retirement planning, use the dedicated retirement or 401(k) calculators.

An emergency fund and a long-term savings pot answer different questions, even though they can sit in the same account. An emergency fund is about runway during a gap in income — how many months of essential spending you can cover with zero contributions coming in. For that question, set monthly contributions to zero and enter only your essential expenses: rent or mortgage, utilities, groceries, insurance, and minimum debt payments. The years-lasting figure, multiplied by twelve, is your number of months of cover.

Long-term savings, by contrast, usually assumes you keep working and contributing while also spending from the same balance — saving for a house deposit while still paying rent, for example, or building a cash cushion alongside ordinary living costs. That calculation cares about the relationship between your contribution and your spending, not just your spending alone, because the contribution is doing real work to offset the withdrawal every month.

The two kinds of "runway thinking" lead to different decisions. For an emergency fund, the goal is usually a fixed target — three to six months of essential spending — after which you stop adding money and let it sit. For long-term savings, the goal is often an ongoing balance between what you put in and what you take out, which is exactly what the break-even point below describes.

Of all the inputs, monthly spending has the largest and most direct effect on how long a balance lasts. Because the simulation subtracts your withdrawal every single month, doubling your spending roughly halves the number of months before the balance reaches zero, all else being equal — the relationship is close to linear once contributions and interest are small relative to the withdrawal.

That's different from a growing investment portfolio, where a large enough balance can make a withdrawal look small by comparison. With a modest cash balance and no growth to speak of, spending is essentially the whole story: the balance is a bucket, and withdrawals are the hole in the bottom.

The calculator defaults to a 3% annual return, applied monthly at one-twelfth of that rate. That figure is meant to represent a cash-like account — a high-yield savings account or a short-term deposit — where the balance itself doesn't fluctuate in value from one month to the next. It is a starting point, not a forecast: savings account rates move with the broader interest rate environment, and yours may be higher or lower. Change the field to match whatever rate your actual account pays.

The rate matters most when your spending is close to what your balance can generate in interest each month. On a $40,000 balance at 3%, interest comes to about $100 a month — a small amount next to typical spending, which is why cash savings rarely last indefinitely unless contributions are doing most of the work. On a much larger balance, or at a meaningfully higher rate, interest alone can start to matter, and the gap between 2% and 4% can be the difference between a shrinking balance and a stable one.

Every month, the simulation adds your contribution and interest, then subtracts your spending. When contribution plus interest is less than spending, the balance shrinks a little every month, and eventually reaches zero. When contribution plus interest is equal to or greater than spending, the balance holds steady or grows, and the calculator reports an infinite runway.

That crossover is the break-even point, and it's worth finding deliberately rather than by accident. Take the default scenario: a $40,000 balance earning 3% generates about $100 of interest in the first month. Against $3,500 of monthly spending, a $500 contribution leaves a net drain of about $2,900 a month, and the balance is gone in a little over a year. Raising the contribution to roughly $3,400 a month — enough that contribution plus interest matches spending — flips the picture to an indefinite runway at that starting balance. Contributions below that line extend the runway; contributions at or above it reverse the direction the balance is heading entirely.

This calculator works in nominal dollars: the balance and spending figures you see are not adjusted for rising prices. That matters because cash sitting at a fixed interest rate can lose purchasing power even while the account balance grows, if inflation runs higher than the rate you're earning. A 3% return against 3% inflation preserves the number on the statement but not what that number can buy.

In practice, this means the monthly spending figure you enter today probably won't buy the same things several years from now. If you want to approximate that effect, periodically increase the monthly spending input to reflect rising costs and re-run the projection, rather than assuming a single fixed number holds for the entire runway.

A savings account return and an investment return are not interchangeable, even when the numbers look similar. A savings account balance generally doesn't fall in nominal value, is available on short notice, and — up to relevant deposit-insurance limits — isn't exposed to market losses. That stability is exactly why 3% is a reasonable cash-like default here.

An investment return, by contrast, comes with volatility: the balance can rise well above 3% in a good year and fall below zero in a bad one, and money tied up in investments may take time to access without selling at an unfavorable moment. This calculator applies one smooth, unchanging rate every month, which fits a cash account far better than a portfolio whose value moves unpredictably. If your savings are actually invested, treat any result here as a simplified illustration, not a projection of market performance — for that, model a range of return assumptions rather than a single number.

Example 1 — Emergency fund. $15,000 in savings, no contributions, essential spending of $4,000 a month, earning 3%. Interest on this balance is trivial next to the withdrawal, so the fund covers spending for about four months before it's exhausted — a useful number to compare against the standard three-to-six-month guideline.

Example 2 — Default scenario. $40,000 in savings, contributing $500 a month, spending $3,500 a month, at a 3% return, starting at age 32. The $100 or so of monthly interest and the $500 contribution together don't come close to matching $3,500 of spending, so the balance depletes in roughly 1.2 years — around age 33.

Example 3 — Reaching break-even. Same $40,000 balance and $3,500 of monthly spending at 3%, but the contribution rises to about $3,400 a month. Contribution plus interest now equals spending, so the balance no longer shrinks — the calculator reports an infinite runway under those exact assumptions, meaning the balance holds steady rather than growing or falling.

The projection advances in monthly steps, for up to 70 simulated years. In each step, the current balance is multiplied by one- twelfth of your annual return, then your monthly contribution is added and your monthly spending is subtracted, in that order. The result becomes the balance carried into the next month.

After each step, the balance is tested: once it falls to zero or below, it's held at zero and the month it happened in is recorded as the depletion point. The years-lasting figure is that month count divided by twelve. If your contribution plus the interest generated at your starting balance is enough to match or exceed your spending, the calculator instead reports an infinite runway (∞) and stops projecting a depletion date, since the balance isn't expected to reach zero.

The chart plots the balance every three months for readability, plus the exact depletion point when one exists. All figures are nominal dollars, rounded for display, and the model treats contribution, spending, and rate as fixed for the entire projection rather than varying year to year.

This is a simplified planning tool, not a forecast. In particular, it does not account for:

• Interest rates changing over the projection period
• Taxes owed on interest earned, which reduce your effective return
• Account fees, minimum balance requirements, or tiered rates
• Irregular or lumpy spending, such as annual bills or one-off purchases
• Inflation eroding the purchasing power of a fixed spending figure
• Unplanned emergencies that require withdrawing more than modeled
• Changes to your income or contribution amount over time

Every result here is an estimate built from the numbers you entered. Revisit the calculator whenever your balance, rate, contribution, or spending changes meaningfully.