How much Bitcoin do I actually need to retire?

It depends on your spending, horizon and assumed return: there is no single number. This calculator runs your own inputs through a year-by-year simulation and shows the exact BTC figure for your case, plus what happens if the assumption turns out too optimistic.

What does the combined default assumption actually do?

It blends two models by taking their geometric mean, year by year: declining returns (Bitcoin's 4-year cycles keep decaying, as they have since 2012) and the power-law trend (Bitcoin's ~15-year price curve keeps its shape). The 50/50 weighting is our own editorial choice, and the tool always shows the range between both extremes next to the blended figure.

Why does the declining-returns extreme keep shrinking over time?

Because that's what Bitcoin's own history shows: each 4-year cycle since 2012 has returned roughly half of the previous one's annualized rate. Extrapolating an early, high-growth rate forever is the most common mistake in informal Bitcoin retirement math.

Is this financial advice?

No. It's a simulation over assumptions you control, using real historical data for the CAGR figures and the stress test: never a prediction of what Bitcoin will actually do, and never a recommendation to buy, hold or sell any amount.

What is the sanity check about?

It converts your assumption into an implied Bitcoin market cap at the end of your horizon, deflates it by your own inflation rate, and compares it against total documented global wealth ($471 T, UBS Global Wealth Report 2025). If it implies Bitcoin alone would be worth more than everything else in the world combined, it flags that.

Why use average cost instead of FIFO for taxes?

To keep the simulation tractable across decades of monthly contributions. Spanish tax law requires strict FIFO lot ordering, covered in detail in our Bitcoin taxes in Spain guide: for an exact figure on your real purchases, that FIFO rule is what applies, not this simplification.

How much Bitcoin do you need to retire?

Type your numbers and this calculator tells you how much BTC you need today, on top of your monthly contribution, to cover your entire retirement. The return assumption is computed live from real price history, never picked by hand.

Your numbers

Current age

Retirement age

Years in retirement

Desired annual spending, in today's dollars

BTC you already hold

Monthly contribution ($)

Annual inflation (%)

Tax on sale

Return assumption

Your result

BTC needed today

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BTC once you reach retirement

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Implied BTC price at the end

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Implied market cap (in today's money)

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Does your current plan hold? —

Stress test (2018): —

Stress test (2022): —

Year by year, through retirement

Once you reach retirement with your current BTC and contributions (under the assumption you picked), this is what each year of drawdown looks like:

Year	Age	Assumed return	Nominal spending	BTC sold	Tax paid	BTC left
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BTC needed, by retirement age

Same spending, contributions and assumption; only the retirement age changes. Your own choice is highlighted.

Retirement age	BTC needed today
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How it's calculated

The simulation runs one year at a time. During your saving years, your monthly contribution buys BTC at that year's projected price; nothing is sold. From retirement onward, each year sells just enough BTC to cover that year's spending (your target amount, compounded forward by your chosen inflation rate) after tax, using a weighted-average cost basis across everything you've ever bought. That's a simplification: Spanish tax law requires strict FIFO lot ordering, covered in full in our Bitcoin taxes in Spain guide. BTC you already hold is treated, for cost-basis purposes only, as if bought today at today's price, since the tool has no way of knowing what you actually paid for it.

The return assumptions, and where each number comes from

Five fixed historical windows (15, 10, 8, 5 and 4 years) give Bitcoin's real compound annual growth rate (CAGR) up to today: 90.5% over 15 years, 63.9% over 10, 37.9% over 8, 14.4% over 5 and 44.9% over 4. Picking one applies that single rate, unchanged, to every year of the horizon: useful for comparison, but naive over decades, since it assumes Bitcoin keeps compounding at a young-asset rate forever.

Declining returns assumes Bitcoin's 4-year, halving-aligned cycles keep decaying as they have so far: 204.1% (2012→2016), 102.0% (2016→2020), 55.8% (2020→2024), an average decay factor of 52.4% per cycle. From the last closed cycle, the model applies that same factor once per cycle: 29.2% in 2024→2028, 15.3% in 2028→2032, 8.0% in 2032→2036, then a floor of inflation plus 2 points from 2036→2040 onward (4.5% with today's default 2.5% inflation).

Power law: trend and floor

Power law assumes price(d) = a × d^b, where d is the number of days since Bitcoin's genesis block (January 3rd, 2009). a and b are fit live, by log-log least squares regression, over the 5,885 days of real price history to date: a ≈ 6.15e-17, b ≈ 5.603, with a standard deviation of the log residuals of ≈ 0.69. Trend is that central fit; Floor shifts the same line down to the 5th percentile of those residuals, a conservative lower band. Because b is smaller than the exponent of time itself, the implied annual growth rate shrinks by construction as the curve ages, with no explicit floor. Today's price sits 38.9% below the trend line; this tool converges that gap to zero linearly over 4 years, then follows the curve. Illustrative trend prices: ≈$1.46 M in 2036, ≈$8.54 M in 2046 (floor variant: ≈$637,687.64 and ≈$3.73 M). None of this is a forecast: it's what a ~15-year-old curve says if the same shape holds.

Combined (the default)

Combined, selected by default, takes the geometric mean of the declining-returns price path and the power-law-trend price path, year by year: combined price = √(declining price × trend price). It's the geometric mean, not a plain average, because these are compounding growth rates, and the geometric mean of two price paths equals the average of their log-returns. The 50/50 weighting is our own editorial choice, not a derived figure. Because both models are expressed as year-over-year percentage rates, the blended path also feeds the stress test: when the first retirement years are replaced by the real 2018 or 2022 sequence, the model resumes applying its own rate to whatever price the crash left behind.

Custom lets you type your own flat annual rate, applied the same way as the fixed windows.

The sanity check: is the assumption even possible?

Any assumption implies a Bitcoin price at the end of your horizon, and multiplying that by 21 million (the maximum supply) gives an implied market cap. To compare a figure decades away against something dated today, this tool deflates that cap by your own inflation rate before comparing it to total global household wealth: $471 T as of 2024, across the 56 markets covering over 92% of the world's wealth, per the UBS Global Wealth Report 2025. If the implied cap, already in today's money, exceeds that figure, the assumption is arithmetically impossible: it would mean Bitcoin alone is worth more than every other asset on Earth. With the combined assumption, this check runs against all three price paths and names which one, if any, breaks it.

The stress test: what if the crash hits on day one of retirement?

A return assumption smooths everything into a single average rate, hiding "sequence risk": a crash right as you start selling forces you to sell far more BTC at depressed prices than the same average return spread evenly would. This tool replays your plan substituting the first four retirement years with what Bitcoin's price really did starting in 2018 (-72.9%, 91.8%, 304.3%, 59.6%) or 2022 (-64.3%, 155.6%, 121.1%, -6.3%), then resumes the chosen assumption from year five. In both real sequences the crash years were followed by strong rebounds, so the four-year total can end up higher than a flat assumption would give, meaning this test can need the same BTC or fewer, not more. Passing it says nothing about a slower, grinding decline instead of a sharp crash and rebound.

A full worked example

Someone aged 40 today, retiring at 60 (20 years of contributions), planning for 25 years of retirement, spending $30,000.00 a year in today's money, already holding 0.50 BTC and contributing $300.00 a month, with 2.5% inflation and no tax applied, needs 0.1093 BTC today under the combined default (computed live as of September 27, 2026): between 0 BTC (your contributions alone are enough) under the power-law-trend optimistic extreme and 1.5403 BTC under the declining-returns conservative extreme. That figure is less than the 0.50 BTC and monthly contributions already in this example, which comfortably cover the full 25 years. Facing the real 2018 crash sequence right at retirement instead of the assumption, that same amount still lasts the full 25 years.