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 required to use it. If you want your scenarios on more than one device, an optional Premium account syncs them for you.
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.
The simulation runs in your browser. Used anonymously, nothing is sent to a server: your scenarios live in your browser's local storage, you can run the planner incognito, on a flight, behind a corporate proxy, or completely offline (it's a Progressive Web App), and you export your data yourself if you want a backup. If you sign in to a Premium account, your profile also syncs to Excelergy's UK-hosted API so it follows you across devices; see the Legal page for the data detail.
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.
- Monte Carlo (optional): 2,000 scenarios with configurable return and volatility assumptions, reported as a success rate and distribution of outcomes.
- Sequence-of-returns stress test (Premium): overlay an early-years market shock on the deterministic path.
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.
- 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
No analytics, no tracking pixels, no third-party scripts. The page is plain HTML/CSS/JavaScript. Used anonymously, Excelergy runs entirely in your browser: scenarios save to localStorage under the excelergy_* namespace and nothing is transmitted anywhere.
An optional Premium account syncs your profile across your devices through api.excelergy.co.uk, hosted in the UK on a Plesk-managed server, with per-user keys encrypting your data at rest. Email address and sign-in codes are the only identifiers held; no password is stored. You can export or delete your profile from the Account drawer at any time. The Legal page has the full data story.
Prefer not to have an account? Use the Export button in the Scenario card to back your scenarios up to a JSON file and Import to restore them on another device. That's the entire data-transfer story for anonymous users.
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.