The savings withdrawal calculator above answers a simple, practical question: if you start with a certain amount of cash and pull out a fixed amount every month, how long does it actually last? This isn't a retirement-specific tool β it's built for anyone drawing down a lump sum for a defined stretch of time, whatever the reason.
Arb Digital built this calculator because "how long will my savings last" is one of the most common financial questions people ask themselves, yet most calculators online bury it inside retirement-only assumptions that don't apply to a career break, a business runway, or a temporary gap in income.
What This Calculator Does
This tool simulates your account balance month by month. Each month, it applies your expected interest or investment return to whatever balance remains, then subtracts your monthly withdrawal. It keeps repeating that cycle until the balance hits zero, then reports back exactly how many months and years that took. If you enable the optional inflation toggle, your withdrawal amount itself grows a little each year, mimicking the reality that a fixed dollar withdrawal buys less over time.
Alongside the "how long" answer, the calculator reports the total dollars you'll withdraw over that period, how much interest your money earned along the way while it was shrinking, and β perhaps most usefully β the maximum monthly amount you could withdraw and never run out at all, known as the perpetual withdrawal threshold.
How to Use It
- Enter your starting balance. This is the lump sum you're planning to draw down β savings, a severance payout, an inheritance, or business capital.
- Enter your planned monthly withdrawal. The fixed dollar amount you intend to take out each month to cover expenses.
- Enter your expected annual interest or return. Even a basic high-yield savings account or money-market fund earns something; enter that expected rate.
- Optionally check "increase withdrawals with inflation." This models a more realistic scenario where your monthly spending need rises over time rather than staying perfectly flat.
- Read your results. The big number shows how long your money lasts; the grid breaks down total withdrawn, interest earned, the perpetual-withdrawal ceiling, and the precise time to depletion.
The Formula / How It's Calculated
Each month, the calculator applies your monthly interest rate (annual rate divided by 12) to the current balance, then subtracts your withdrawal for that month. That new balance carries into the next month, and the process repeats until the balance reaches zero. This month-by-month compounding approach is more precise than a simple average, since it correctly captures how a shrinking balance earns proportionally less interest as time goes on.
The perpetual-withdrawal threshold β the amount you can take out every month without ever depleting the principal β is calculated as your balance multiplied by the monthly interest rate. Withdraw exactly that amount, and in theory the interest earned each month exactly replaces what you take out, leaving the principal untouched indefinitely. For a broader look at how compound interest and account drawdowns work, the U.S. Securities and Exchange Commission's Investor.gov offers a plain-language primer.
The Bridge-Period Problem
Not every savings drawdown is about retirement. Plenty of people need to know exactly how long a lump sum will cover them during a defined bridge period: a sabbatical from work, a career change with a gap before the next paycheck, the months before a pension or Social Security benefit finally kicks in, or simply living off savings while a new business ramps up toward profitability. In every one of these cases, the core question is identical β not "will this last forever," but "will this last exactly as long as I need it to, and not a day less."
That distinction matters because the right strategy for a bridge period is different from a lifetime retirement strategy. If you know your gap is 18 months, you don't need your withdrawal rate to be sustainable forever β you need it to be sustainable for exactly 18 months, which often means you can safely withdraw far more aggressively than any long-horizon retirement rule would ever recommend.
The Perpetual-Withdrawal Threshold
There's a special case worth understanding on its own: the withdrawal rate at which your balance never actually shrinks. If your monthly withdrawal is smaller than or equal to the interest your balance earns that month, your principal stays intact indefinitely β you're living entirely off the returns, not the underlying capital. This calculator surfaces that exact number so you can see how far your current withdrawal plan sits from true sustainability, even if "forever" isn't actually your goal.
Understanding this threshold is useful even for short-term drawdowns, because it tells you how much of your monthly withdrawal is "using up" principal versus simply collecting interest you've already earned. A withdrawal rate well above the perpetual threshold depletes savings fast; one close to it barely dents the balance at all.
Why a Low-Return Parking Spot Shortens Your Runway Fast
Where you park a lump sum you're drawing down matters more than most people expect. A balance earning 0.5% in a checking account has almost no cushion against your monthly withdrawals β nearly every dollar you take out comes straight from principal. Move that same balance into an account or fund earning 4-5%, and a meaningful share of each withdrawal is effectively coming from earned interest instead, meaningfully extending how long the money lasts.
This doesn't mean chasing high returns with money you need on a strict timeline β liquidity and safety matter enormously for near-term withdrawals. But it does mean it's worth checking whether idle cash sitting in a low-yield account is quietly shortening your runway for no good reason.
Bridge Fund vs. Emergency Fund: Two Different Jobs
It's worth distinguishing a planned drawdown, like the one this calculator models, from a true emergency fund. An emergency fund exists for the unplanned and unpredictable β a sudden job loss, a medical bill, an urgent home repair β and should generally sit somewhere highly liquid and low-risk, ready to be tapped without notice. A bridge fund, by contrast, is drawn down on purpose, over a known or estimated period, toward a specific goal you've already decided on: a sabbatical, a career transition, or a gap before other income begins.
Because a bridge fund's timeline is at least roughly known in advance, it can sometimes tolerate slightly more return-seeking risk than a true emergency fund, provided the money isn't needed on an unpredictable moment's notice. Understanding which job your savings balance is actually doing changes how aggressively you should invest it while you draw it down.
Practical Ways to Extend Your Runway
If this calculator shows your money running out sooner than you'd like, there are really only a few levers available, and it helps to see them listed together: reduce the monthly withdrawal amount, extend the timeline by finding even partial income during the drawdown period, move the balance into a higher-yielding but still safe account, or delay the start of the drawdown to let the balance grow a bit longer first. Testing combinations of these levers directly in the calculator β a slightly lower withdrawal paired with a slightly higher-yield account, for instance β often reveals that a comfortable runway is closer than it first appeared.
Common Mistakes to Avoid
- Ignoring interest entirely. Even a modest return meaningfully extends how long a balance lasts versus a 0% assumption.
- Assuming your withdrawal need will stay perfectly flat. Real expenses tend to drift upward; the inflation toggle in this tool models that more realistically.
- Parking drawdown cash in a 0.1% checking account. A safe, higher-yield account or fund can meaningfully extend your runway without adding real risk.
- Confusing a bridge-period drawdown with a lifetime retirement plan. The right withdrawal rate depends entirely on how long you actually need the money to last.
- Forgetting taxes on interest or investment gains. Depending on the account type, earned interest or gains may be taxable in the year received.
If this is retirement income rather than a shorter bridge period, our 4%-rule-based Retirement Withdrawal Calculator is built specifically for that.
Retirement Withdrawal Calculator All Free ToolsRelated Free Tools From Arb Digital
If your drawdown is specifically for retirement, see our Retirement Withdrawal Calculator, which models the 4% rule with inflation-adjusted raises over a full retirement horizon. Also check the Retirement Calculator and FI Number Calculator to see your broader savings targets, plus the Social Security Benefits Calculator and Pension Calculator for guaranteed income sources. Browse everything in our free online tools hub.
Frequently Asked Questions
It depends on your starting balance, your withdrawal amount, and the interest or investment return your balance earns while you draw it down. This calculator simulates the balance month by month to give you an exact figure.
It's the maximum monthly amount you could withdraw without ever depleting your principal β calculated as your balance multiplied by your monthly interest rate. Withdraw at or below this amount and, in theory, the balance never shrinks.
No. This tool is a general-purpose cash drawdown calculator for any purpose β a sabbatical, a career gap, a business runway β with no retirement-specific assumptions. For retirement-specific 4%-rule modeling, use our dedicated Retirement Withdrawal Calculator instead.
If your monthly expenses are likely to rise over the drawdown period, checking the inflation toggle gives a more realistic picture than assuming a perfectly flat withdrawal amount for the entire period.
Yes. A higher-yield, liquid account or fund lets interest offset more of your monthly withdrawal, extending your runway compared to a low-yield checking account, without necessarily adding meaningful risk.
No. It models pre-tax balance growth and withdrawals only. Interest or investment gains may be taxable depending on your account type and jurisdiction.
This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.
