About Excelergy
A UK retirement calculator that shows its working.
Excelergy is a free year-by-year retirement planner for UK pensions and ISAs. The numbers behind the projection are visible by default - the ledger shows tax, NI, drawdown, auto-crystallisation, and pot balances row by row. No black box, no sign-up, no data leaves your browser.
Why this exists
Most pension calculators do one of two things: produce a single optimistic headline ("you'll have £X at 65") with no working shown, or restrict you to a single scenario at a time so you can't compare alternatives. The interesting questions (Do I retire at 60 or 67? Drawdown or annuity? Pension first or ISA first?) are usually the ones that get hidden.
Excelergy was built to make those answers tractable. The engine simulates pension and ISA pots year by year using the actual UK tax rules - personal allowance, the £100k taper, basic/higher/additional rates (UK and Scottish), the Lump Sum Allowance, NI on employment income, UFPLS-style drawdown - and shows the full ledger so you can see where every pound came from and where it went.
It's deliberately client-side: the entire simulation runs in your browser. Nothing is sent to a server. You can use it incognito, on a flight, behind a corporate proxy, or while completely offline (it's a Progressive Web App). Your scenarios live in your browser's local storage; you export them yourself if you want a backup.
What it does
- Year-by-year simulation from your current age to your end age, accounting for salary growth, contributions, employer match, salary sacrifice, growth, charges, inflation, and retirement spending.
- Pension mechanics: crystallisation (25% tax-free + 75% taxable), the £268,275 Lump Sum Allowance, UFPLS-style drawdown, flexi-access lump-sum strategy, and the post-2028 access-age change.
- ISA mechanics: Cash ISA, Stocks & Shares ISA, the £20,000 allowance, the post-2027 £12,000 Cash ISA cap for under-65s, and drawdown order (pension first vs ISA first).
- State Pension: SPA schedule, statePensionGrowth assumption, and deferral (1% per 9 weeks).
- Annuities: level or RPI-linked, with the income line shown separately in the ledger and taxed alongside the State Pension.
- Tax: full UK and Scottish income-tax bands, the £100k Personal Allowance taper, PA overrides for non-standard tax codes, and Class 1 NI on employment income.
- Scenario tooling: duplicate scenarios for A/B testing, overlay two on the chart for side-by-side comparison, export and import as JSON, load five sample scenarios.
- Stress testing: simulate a one-off market crash at a chosen age to see how pots recover.
What it deliberately doesn't do
To stay understandable and within the FCA introducer exemption, Excelergy avoids:
- Recommendations. No "best SIPP", no comparative ratings, no "you should..." framing. Provider listings on the planner and FAQ are signposts only.
- Personalised advice. The calculator doesn't know your full circumstances. Specific decisions need a regulated adviser.
- Monte Carlo / sequence-of-returns risk. The single-rate model is the deliberate trade-off for understandability - you can still test fragility with the crash-year stress test.
- Defined benefit pensions. Final-salary schemes are too case-specific to model generically; their cash equivalent transfer values need an adviser.
- Inheritance tax planning, GIA capital gains tax, property income, the tapered annual allowance for high earners, and MPAA restrictions after flexible drawdown. All listed in the FAQ as out of scope.
Who builds it
Excelergy is built and maintained by Paul Payne, an IT professional in the UK with a long-standing interest in personal finance and an opinion that most retirement tools obscure rather than clarify. The site is independent: it doesn't take adviser commissions, doesn't push a particular provider, and isn't sponsored by anyone. The intent is to keep it that way.
Tax-figure updates happen annually around the April tax-year change. Engine changes (new mechanics, bug fixes) are versioned and visible in the footer build stamp. The FAQ records what's in scope and what's deliberately not.
Privacy
Excelergy is fully client-side. There is no backend, no analytics, no tracking pixels, no cookies beyond what your browser sets locally. The page is plain HTML/CSS/JavaScript; everything runs in your browser. Your scenarios are saved in your browser's localStorage under the excelergy_* namespace and never transmitted anywhere.
Use the Export button in the Scenario card to back your scenarios up to a JSON file. Use the Import button to restore them on another device. That's the entire data-transfer story.
Tech
HTML, CSS, vanilla JavaScript. No frameworks. The simulation engine (planner-engine.js) is pure and testable; the test runner is at /test.html if you want to see it pass. A Service Worker caches the assets for offline use and to keep things fast.
Get in touch
Bugs, suggestions, questions, or factual corrections: email info@excelergy.co.uk. The feedback envelope icon in the topbar opens the same address.