Retirement Calculator Guide
The Retirement Calculator projects what your pension or retirement pot could be worth on the day you stop working. It compounds your savings monthly, adds employer money on top, drags the result down by fees, and shows the answer both in future cash and in today's money so you can see what it will actually buy.
It covers the UK wrappers: workplace pensions, SIPPs and ISAs, with auto-enrolment employer money and tax relief worked out for you.
It covers the US wrappers: 401(k) and IRA, with the employer match worked out for you.
It also sets a retirement income target, prices the pot that target requires, and tells you whether your current plan gets there, and if not, what closes the gap. The region toggle switches the currency, account types and income benchmarks.
How to Use
- Current age and retirement age: Set both sliders. The gap between them is your saving horizon, and it matters more than almost anything else.
- Current pot: What you have saved for retirement already, across all accounts.
- Monthly contribution: What you personally pay in each month.
- Account type: Pick the wrapper your savings live in. For a workplace pension, enter your salary and the calculator works out the employer money and the tax relief for you; a SIPP gets relief only; an ISA gets neither. Pick "None / custom" to type a flat monthly boost yourself.
- Retirement income target: Pick a PLSA living standard (single or couple) or enter a custom income. The calculator turns the income into a target pot and shows your gap or surplus.
- Account type: Pick the wrapper your savings live in. For a 401(k), enter your salary and match details and the calculator works out the employer money for you; an IRA has no match. Pick "None / custom" to type a flat monthly boost yourself.
- Retirement income target: Enter your income and set a replacement rate. The calculator turns the income into a target pot and shows your gap or surplus.
- Expected annual growth: The average yearly return you expect before fees. 6% is a common long-run assumption for a diversified portfolio.
- Annual fees: Fund and platform charges as a percentage of your pot. The default of 0.4% is typical for low-cost index funds plus a platform.
- Inflation: Used to translate the future pot into today's buying power. 2.5% sits near most central bank targets plus a margin.
Understanding the Results
- Pot at retirement (nominal): the headline number, in future cash. It will look big because decades of inflation are baked into it.
- Pot in today's money: the same pot deflated by your inflation assumption. This is the number to plan around, because it is expressed in buying power you understand now.
- You contributed: the total of your own monthly payments over the whole horizon.
- Employer money and tax relief: what landed in the pot alongside your contributions without coming out of your pocket.
- Growth earned: investment returns, net of fees. Over long horizons this usually dwarfs what you paid in.
- Lost to fees: the gap between your projected pot and the same projection with zero fees. It includes the growth those fees would have earned, which is why it is much larger than the fees themselves.
- Target pot, surplus or shortfall: the pot your income target requires, in today's money, and how your projection compares. When you are short, the table also shows the extra monthly contribution that closes the gap and the earliest retirement age that closes it without paying in more.
The chart plots both the nominal and the today's-money series by age, so you can watch the two lines diverge as inflation compounds.
Setting a Target: How Much Is Enough?
The calculator prices your target with the 25x rule. If a pot can sustainably pay out about 4% of its starting value each year, then the pot you need is your required private income multiplied by 25. The 4% figure comes from historical safe withdrawal rate research; our Safe Withdrawal Calculator digs into where it comes from and when it breaks.
PLSA Retirement Living Standards. Pensions UK (formerly the PLSA) publishes Retirement Living Standards describing what retirement costs at three levels, for one-person and two-person households. The June 2026 update puts them at, per year: Minimum £13,900 single / £22,500 couple, Moderate £32,700 / £45,400, and Comfortable £45,400 / £62,700. The figures exclude housing costs and income tax. Pick a standard in the calculator, or enter a custom income. Need £20,000 a year from your savings? That points to a £500,000 pot.
Replacement rate. A common way to set a target is as a share of your pre-retirement income. The Social Security Administration notes that financial advisors often suggest replacing about 70 to 80 percent of pre-retirement earnings; the calculator defaults to 80% and lets you set anywhere from 50% to 100%. People with paid-off homes and modest plans land lower; big travel plans push it higher. Need $20,000 a year from your savings? That points to a $500,000 pot.
State provision is subtracted first. Your private pot only has to fund the income the state does not.
With the toggle on, the calculator subtracts the full new UK State Pension of £12,548 per year (gov.uk, 241.30 GBP per week, 2026/27 tax year) from your target income before applying the 25x rule.
With the toggle on, the calculator subtracts the average US Social Security retired-worker benefit of $24,974 per year (ssa.gov Monthly Statistical Snapshot, $2,081.16 per month, April 2026) from your target income before applying the 25x rule. Your own Social Security benefit depends on your earnings record, so check your statement at ssa.gov for a personal figure.
How the Account Type Changes the Math
Money that lands in your pot but did not come out of your pocket is the cheapest retirement saving there is, and it depends on the wrapper:
UK workplace pension. Your employer must contribute at least 3% of qualifying earnings under auto-enrolment (within an 8% total minimum, gov.uk), and your own contributions get basic-rate tax relief: each £80 you pay in becomes £100 in the pot, so £100 of pension costs you £80. Enter your salary and employer percentage and the calculator adds both effects.
UK SIPP. No employer money, but the same basic-rate relief on your contributions. The pension annual allowance is £60,000 (2025/26 tax year).
UK ISA. No relief on the way in, but withdrawals are completely tax free. The allowance is £20,000 per tax year (2025/26).
Pick "None / custom" to bypass all of this and enter a flat monthly boost yourself.
US 401(k). Many employers match a portion of your contributions; a common arrangement is 50% of what you pay in, up to 6% of salary. That is an instant 50% return on the matched money, which is why "contribute at least to the full match" is near-universal advice. The employee deferral limit is $24,500 for tax year 2026 (IRS).
US IRA. No match. A traditional IRA defers tax until withdrawal; a Roth IRA is funded with after-tax money and grows tax free. The contribution limit is $7,500 for tax year 2026 (IRS).
Pick "None / custom" to bypass all of this and enter a flat monthly boost yourself.
The Compounding Math
The projection compounds monthly at a net rate (growth minus fees) and adds your contributions each month:
where g is annual growth %, f is annual fees %, C is the total monthly pay-in (your contribution plus employer money), and B_n is the balance after month n. The today's-money figure divides the result by (1 + inflation/100)^{years}.
Why Fees Matter So Much
A fee of 1% sounds tiny next to a 6% return, but it removes one sixth of your growth every single year, and the money it removes stops compounding for you. Over a 35 year horizon the difference between 0.4% and 1.5% in annual charges can be a five or six figure sum. The "Lost to fees" row makes this visible: try moving the fees slider and watch it. Cutting fees is one of the few guaranteed ways to retire with more.
UK Accounts at a Glance
The two main wrappers are pensions and ISAs. The ISA allowance is £20,000 per tax year and the pension annual allowance is £60,000 (gov.uk, 2025/26). Under auto-enrolment, a minimum of 8% of qualifying earnings goes into your workplace pension, of which at least 3% comes from your employer. Pension contributions receive tax relief, so each £80 you pay in becomes £100 in the pot at the basic rate.
US Accounts at a Glance
Tax-advantaged saving happens mostly through a 401(k) and an IRA. For tax year 2026 the IRS set the 401(k) employee deferral limit at $24,500 and the IRA contribution limit at $7,500 (IRS newsroom, November 13, 2025). Many employers match a portion of your contributions, commonly 50% of what you pay in up to 6% of salary. Always contribute at least enough to capture the full match: it is an instant, risk-free return.
Assumptions and Limitations
- Returns, fees, and inflation are held constant every year. Real markets are lumpy, and the sequence of returns matters in ways a steady-rate model cannot show.
- Contributions are assumed to stay flat in cash terms. In practice most people increase them as earnings rise, so the projection is conservative on that front.
- The calculator ignores taxes on withdrawal and does not enforce contribution limits.
- The State Pension figure is the current published flat rate; your own entitlement may differ. The 4% withdrawal rate behind the 25x rule is a planning rule of thumb, not a guarantee.
- Check that your planned contributions fit within the pension annual allowance (£60,000, 2025/26) or ISA allowance (£20,000 per tax year).
- The Social Security figure is a published average; your own benefit depends on your earnings record. The 4% withdrawal rate behind the 25x rule is a planning rule of thumb, not a guarantee.
- Check that your planned contributions fit within the IRS limits: $24,500 for a 401(k) and $7,500 for an IRA (tax year 2026).