Four percent rule calculator
A 1,000,000 portfolio at the classic 4% rate supports about 40,000 a year, or 3,333.33 a month. Turn it around to see the nest egg your spending calls for, and how far your savings fall short of it or exceed it. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Portfolio
- 1,000,000
- Withdrawal rate percent
- 4
- Rate decimal
- 0.04
- Years multiplier
- 25
- Precision
- 2
The four percent rule is the best-known safe withdrawal rate heuristic for retirement planning: withdraw about four percent of your portfolio in the first year, then adjust for inflation, and historically many balanced portfolios survived thirty-year horizons in US market studies. This four percent rule calculator turns that rule into two practical numbers. Enter a portfolio balance to estimate a sustainable annual and monthly withdrawal. Enter desired annual or monthly expenses to estimate the nest egg you need (the classic twenty-five-times multiplier at four percent). Supply both sides to see portfolio gap, coverage ratio, and whether the plan is funded under the chosen rate. You may override the default four percent with another withdrawal rate when you prefer a more conservative three percent plan or a more aggressive five percent trial.
What the four percent rule means and what this calculator returns
The four percent rule grew out of research on how large a constant real withdrawal a diversified portfolio could support over multi-decade retirements without running out of money in the historical samples studied. In plain language, if you need forty thousand dollars of spending per year and you use a four percent withdrawal rate, you need a portfolio of about one million dollars because forty thousand divided by zero point zero four equals one million, which is the same as annual expenses times twenty-five.
Conversely, a one million dollar portfolio at four percent supports about forty thousand dollars of annual withdrawals, or about three thousand three hundred thirty-three dollars per month before taxes and fees. This calculator encodes those two identities exactly: annual withdrawal equals portfolio times rate over one hundred, and required portfolio equals annual expenses divided by rate over one hundred. The years multiplier field is one hundred divided by the rate, so four percent yields twenty-five and three percent yields about thirty-three point three three.
Optional fields let you pass monthly expenses instead of annual ones; monthly is converted with a fixed twelve-month year so results stay reproducible. When both a portfolio and a spending goal are present, the response also includes portfolio gap (portfolio minus required nest egg), coverage ratio (portfolio over required), and a funded flag that is true when the portfolio meets or exceeds the required amount under the chosen rate.
Nothing here forecasts markets, taxes, Social Security, or longevity; it sizes withdrawals and nest eggs under a constant percentage rule so planners, educators, and product UIs share one clear contract.
What you can do with it
Size a first-year retirement withdrawal
Enter a portfolio balance and the default four percent rate to estimate sustainable annual and monthly withdrawals before taxes and fees.
FAQ
How does the four percent rule calculator work?
Provide a portfolio and/or annual or monthly expenses. At 4%, annual withdrawal equals portfolio × 0.04 and required portfolio equals annual expenses ÷ 0.04 (25× spending).
What if I only know monthly expenses?
The response includes both monthly and annual spending fields.
Can I use a rate other than 4%?
Years_multiplier becomes 100 ÷ rate, so 3% implies about 33.33× expenses.
Is this a full retirement simulation?
No. It applies the constant safe-withdrawal-rate identities only. It does not model markets, inflation paths, taxes, Social Security, or sequence-of-returns risk.
How much do I need saved to retire under the four percent rule?
Multiply your yearly spending by 25, which is the same as dividing it by 0.04. If you need 40,000 a year, the rule points to a portfolio of about 1,000,000. A lower withdrawal rate raises the multiplier and the target.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/finance/rule-of-4-percent \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"portfolio":1000000,"nest_egg":1}'const res = await fetch("https://api.kit.forhosting.com/finance/rule-of-4-percent", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"portfolio": 1000000,
"nest_egg": 1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/finance/rule-of-4-percent",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"portfolio": 1000000,
"nest_egg": 1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/finance/rule-of-4-percent", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"portfolio":1000000,"nest_egg":1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"portfolio":1000000,"nest_egg":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/finance/rule-of-4-percent", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"portfolio": 1000000,
"nest_egg": 1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "finance.rule_of_4_percent",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Use it free in the browser or call the API at $0.002 per successful request.
What the four percent rule means and what this calculator returns
The method tag is always rule_of_4_percent even when you customize the rate, because the capability implements that family of safe-withdrawal sizing math rather than a full sequence-of-returns simulator.
Input contract, defaults, rounding, and error behaviour
Precision defaults to two decimal places for currency-style display and may be set from zero to fifteen via precision, decimals, or dp. POST a JSON body with at least one of portfolio, annual_expenses, or monthly_expenses. Portfolio is the investable balance you want to draw from; aliases nest_egg, balance, assets, and principal are accepted. Annual expenses is desired yearly retirement spending; aliases include annual_spending, yearly_expenses, spending, and expenses. Monthly expenses may stand in for annual when you only know a monthly budget; the engine multiplies by twelve and still reports both annual_expenses and monthly_expenses in the success payload. Withdrawal_rate_percent defaults to four and may be overridden with aliases swr_percent, rate_percent, rate, or swr; it must be strictly greater than zero and at most one hundred percent points. Missing all three of portfolio and the expense fields fails with invalid_input naming the need for at least one side. Zero or negative money amounts, non-finite numbers, empty strings, and rates outside the allowed band also fail with invalid_input and are not billed. Successful responses always echo withdrawal_rate_percent, rate_decimal, years_multiplier, method, formula, and precision. Portfolio-only calls add portfolio, annual_withdrawal, and monthly_withdrawal. Expense-only calls add annual_expenses, monthly_expenses, and required_portfolio. Combined calls add the dual-side fields plus portfolio_gap, coverage_ratio, and funded.
Where a four percent rule API earns its keep
Retirement coaches and FIRE-oriented planners use a four percent rule calculator as a first-pass sanity check before deeper Monte Carlo or tax-aware models: clients type a nest egg and see a ballpark annual budget, or type a lifestyle cost and see the savings target. Personal finance educators need a deterministic oracle for homework keys so that twenty-five times spending and four percent of portfolio never disagree across student calculators. Product teams building wealth dashboards embed the same contract so a marketing landing for four percent rule calculator matches the signed-in tool and the backend API without re-implementing edge cases around monthly-to-annual conversion. Spreadsheet users and automation scripts call the API to pin required_portfolio and annual_withdrawal in CI when they refactor goal-based UI copy, ensuring a one million dollar portfolio at four percent still maps to forty thousand dollars a year. Pair the free interactive page for exploration with the priced endpoint for pipelines, and keep custom rates such as three or three point five percent when you teach conservatism without leaving the four percent rule framing that users actually search for.
Integration use cases
Compute the nest egg for a spending goal
Enter annual or monthly expenses to get required_portfolio via the years multiplier (25× at 4%) for goal-based savings targets.
Check coverage with both sides
Supply portfolio and expenses together to see portfolio_gap, coverage_ratio, and whether the plan is funded under your chosen withdrawal rate.
Technical questions
What does the four percent rule calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.