Every FinCalcHub tool for planning retirement in the USA, UK and South Africa — 401(k), Roth IRA, ISA, TFSA, FIRE and the compound-growth maths underneath all of them. Free, instant, no signup.
Retirement is the single largest financial goal most people will ever set, and it is the one where small early decisions matter most. A 25-year-old who puts $300 a month into a diversified portfolio earning 5% in real terms ends up with roughly $445,000 in today's money by age 65. The same person starting at age 35 ends up with around $245,000 — barely more than half — for an identical monthly contribution. That gap is not a market timing problem or a tax problem; it is simply the cost of ten missing years of compounding.
What makes the maths counter-intuitive is that compounding is back-loaded. In the first ten years, your portfolio grows roughly in line with what you put in. In the last ten years before retirement, more than 70% of the growth typically comes from market returns rather than your contributions. People who treat their twenties and thirties as "too early to think about retirement" are giving up the most valuable years, because those are the years that supply the principal the late-stage returns compound on. A retirement calculator forces the trade-off into view: it shows what a $200 a month gap, sustained for 30 years, actually costs you at the end.
Any retirement calculator worth using has to answer five questions, and most generic ones only answer two. The first is how much do I need? The standard answer is 25 times your expected annual spending in today's money — the inverse of the 4% safe withdrawal rate popularised by the Trinity study. If you expect to spend $40,000 a year, you need a $1 million pot. If you expect £30,000, you need around £750,000. The second is how much should I save each month? This is where most off-the-shelf tools stop, because the answer depends on the next three questions.
The third is what return assumption am I making? Use a real (after-inflation) return so the final number is in today's money. The fourth is which tax wrapper am I using? A dollar inside a 401(k), Roth IRA, ISA, SIPP, RA or TFSA grows much faster than a dollar in a taxable brokerage account, and the wrapper changes both your effective contribution and your withdrawal options. The fifth is when can I actually retire? — which depends on all of the above plus your savings rate. A serious calculator lets you flex savings rate and watch the retirement age curve respond.
The mechanics of compounding are universal, but the wrappers that determine how much of each dollar, pound or rand actually compounds are deeply regional. Pick the wrong wrapper for your country and you can easily forfeit 1–2 percentage points of net return every year for decades — a difference of hundreds of thousands at retirement.
The American system is built around employer plans and individual accounts. A 401(k) lets you defer income tax on contributions up to the IRS annual cap, plus a catch-up amount once you turn 50. Most employers match a percentage of your salary — that match is the closest thing to free money in personal finance, and is the reason "capture the match first" is universal advice. Roth IRAs flip the tax treatment: you contribute post-tax dollars, but all growth and withdrawals in retirement are tax-free. Traditional IRAs sit between the two. Model each wrapper on its own page to see which combination wins for your income.
The UK splits retirement saving between an ISA (£20,000 annual allowance, post-tax in, tax-free growth and withdrawals) and a SIPP or workplace pension (tax relief on contributions, taxable withdrawals with 25% tax-free lump sum). Workplace pension auto-enrolment captures most employees, with the employer typically contributing 3% and the employee 5%. ISAs are unmatched for flexibility — no withdrawal restrictions or income-tax-on-the-way-out — which makes them the natural FIRE wrapper for UK savers planning to retire before State Pension age.
South Africans get a tax deduction on Retirement Annuity (RA) contributions up to 27.5% of taxable income (capped at R350,000 per year), with the pot growing tax-free inside the wrapper but taxed on withdrawal. The TFSA wrapper, governed by SARS s12T, allows R36,000 a year and R500,000 lifetime in completely tax-free growth — small contributions but huge over decades. Most SA savers should use both: the RA to drop their marginal tax bracket today, the TFSA as the long-run compounder for tax-free withdrawals later.
Pick the tool that matches the question you're actually asking. All run in your browser, all support USA, UK and SA where relevant.
A common rule of thumb is 25 times your expected annual spending in today's money — the inverse of the 4% safe withdrawal rate. If you expect to spend $40,000 / £30,000 / R600,000 per year, you'll need roughly $1m / £750,000 / R15m in invested assets. Run the numbers in the retirement savings calculator to pressure-test your own figure against your real return, tax wrapper and retirement age.
For a globally diversified equity portfolio, a 5% real return (after inflation) is a reasonable long-run base case for 30-plus year horizons — equivalent to roughly 7–8% nominal at typical inflation. Use a lower number (3–4% real) for stress tests and dial the nominal return down as you approach retirement and shift towards bonds and cash.
They are not directly comparable — they're the tax-advantaged retirement wrappers for the USA, UK and South Africa respectively. Inside their own country, the priority is usually: capture any employer match first, then max the tax-free wrapper (Roth IRA / ISA / TFSA), then top up the tax-deferred wrapper (401(k) / SIPP / RA) before unwrapped taxable investing.
At a 15% savings rate and 5% real returns, you typically hit a 25x number around age 60–62. Push the savings rate to 25% and you can shave 7–10 years off; drop to 10% and traditional retirement age slips into the late 60s. The FIRE calculator shows the savings-rate-to-years-to-retire curve explicitly.
Yes — always think in real (after-inflation) numbers. A million at age 35 buys roughly half as much at age 65 even at modest 2% inflation. FinCalcHub's retirement calculators default to real returns so the projected pot reflects what it will actually buy you in today's money.
Retirement planning doesn't sit on its own. Your mortgage decision affects how much you can save; your tax wrapper choice affects how much of every contribution actually compounds.
Deeper reads: The 4% rule · How much to save by 35 · Retiring at 55 · Retirement planning in South Africa · UK State Pension · 401(k) employer match · Compound interest explained