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About Selvox

Free \u00b7 UK-specific \u00b7 Honest probability outputs

Over 12 million UK adults are under-saving for retirement. Most free tools either ignore tax entirely, use US return data, or exist to funnel you toward a specific product. Selvox exists because none of the tools we wanted to use actually existed.

The Problem With Existing Tools

Every free retirement calculator available to UK savers has at least one of these problems:

  1. 1

    They use US data

    The famous “4% rule” comes from research on US markets. UK markets have different return characteristics, different inflation history, and a different tax system. A tool built on US S&P 500 data will give UK investors systematically wrong answers.

  2. 2

    They ignore tax

    The interaction between ISAs, SIPPs, State Pension, and the Personal Allowance is complex. The £100,000–£125,140 income range creates an effective 60% marginal tax rate that most tools completely miss. Getting tax wrong can mean the difference between a plan that works and one that doesn’t.

  3. 3

    They give you a single misleading number

    “You’ll have £450,000 at retirement” sounds precise but tells you nothing about the range of possible outcomes. Markets are volatile. Sequence of returns matters enormously. A single projected figure is worse than useless — it gives false confidence.

  4. 4

    They’re sales funnels

    Most “free” retirement calculators exist to sell you a specific platform or product. The recommendation is built in from the start. The tool optimises for your signup, not your retirement.

What Selvox Does Differently

UK-native data
Selvox uses the Barclays Equity Gilt Study (UK equity and gilt returns from 1899), ONS inflation series, and JST Macrohistory Database. Not US data. Not a global average. Actual UK market history going back 125 years.
Full tax engine
We model income tax, National Insurance, the Personal Allowance taper, SIPP drawdown, ISA withdrawals, Capital Gains Tax, and dividend tax. We calculate the optimal drawdown sequence for your specific situation. Tax is not an afterthought — it is central to the calculation.
Honest probability outputs
Instead of a single projected figure, Selvox runs 10,000 simulations and shows you the range of outcomes. “73% chance of lasting to age 90” is an honest answer. “You’ll have £450,000” is not.
Permanently free, permanently ad-free on the calculator
The calculator will never show adverts. It will never be gated behind a paywall. It will never recommend a specific product mid-calculation. We earn revenue through clearly disclosed affiliate referrals on the results page only.
No affiliated fund provider
We do not have a financial product to sell you. We are not owned by a platform, an insurer, or an asset manager. The calculation is not influenced by commercial relationships.

How It Works

When you complete the calculator, Selvox:

  1. 1Takes your inputs and constructs a detailed financial model of your situation — your wrappers, contributions, State Pension entitlement, and spending goals.
  2. 2Runs 10,000 simulations, each using a different randomly sampled sequence of historical UK market returns. Some sequences include the 1929 crash. Some include the 1970s stagflation. Some are benign.
  3. 3In each simulation, it applies UK tax rules year by year, drawing from your wrappers in the optimal order to minimise your lifetime tax bill.
  4. 4It counts how many of those 10,000 simulations result in your portfolio lasting to your target age. That count, expressed as a percentage, is your survival probability.

All of this runs in your browser. Your financial data never leaves your device.

For a detailed explanation of the methodology, see our Methodology page.

What Selvox Is Not

Selvox does not provide regulated financial advice. It provides financial information and guidance. These are legally distinct categories. We model your situation based on the inputs you provide\u00a0\u2014 we do not know your full financial picture, your risk tolerance, your family circumstances, or your specific tax position.

For significant financial decisions\u00a0\u2014 particularly large pension transfers, early retirement decisions, or complex tax planning\u00a0\u2014 please speak to a regulated financial adviser. You can find one at unbiased.co.uk (opens in new tab) or vouchedfor.co.uk (opens in new tab).

We say this not as a legal disclaimer but because we mean it. A good IFA who knows your full situation will give you better advice than any calculator can.

Who Built This

Selvox was built as a tool we wanted to exist for UK retirement planners.

It is independently operated with no institutional backing, no venture capital funding, and no affiliated financial product provider. Revenue comes from clearly disclosed affiliate referrals.

The methodology has been validated against HMRC\u2019s own tax calculator, the DWP State Pension forecast service, and published academic research on UK safe withdrawal rates.

Get Involved

Found a bug in the tax calculation? Disagree with a modelling assumption? Have data we should be using?

We genuinely want to hear from you. The r/FIREUK and r/UKPersonalFinance communities have been invaluable in testing and improving the model.

Email us at hello@selvox.co.uk or visit the contact page for full details.