About UK SIPPs
A Self-Invested Personal Pension (SIPP) is a tax-advantaged retirement account that gives you full investment control - choose individual shares, ETFs, funds, even commercial property. Unlike a workplace pension, you pick the provider and investments.
Tax relief at source: Pay £80 → £100 lands in your SIPP (basic rate added automatically). Higher rate (40%) and additional rate (45%) taxpayers claim the extra 20% / 25% via Self-Assessment, effectively getting £62 / £55 net cost per £100 in SIPP.
Annual allowance 2025/26: £60,000 (or 100% of relevant earnings, whichever lower). Tapers to £10,000 for adjusted income above £260,000. Carry-forward: unused allowance from previous 3 tax years can be used in current year.
Access: Currently age 55 (rises to 57 from April 2028). Take up to 25% tax-free as Pension Commencement Lump Sum, capped at £268,275 (LSA) across all pensions. Rest taxed as income at your marginal rate.
Formula
Future value = compound growth on monthly contribs + current balance
Tax-free lump sum = min(25% of pot, £268,275)
Taxable income = remaining 75% (taxed at marginal rate at withdrawal)
Worked example
Higher rate taxpayer (40%), age 35, retiring at 60. £500/month into SIPP. Current balance £20K. 6% annual growth.
- Monthly £500 (your cash) → £625 grossed up at basic rate in SIPP
- Plus 20% extra (£125) reclaimed via tax return - net cost only £375/mo
- 25 years × £625/month × 6% growth + £20K initial
- Pot at 60: ~£521,000
- 25% tax-free lump = £130,250
- Remaining £390,750 drawn over 25 years = ~£15,630/year, tax at slab
FAQs
SIPP vs ISA - which?
Both tax-free growth. SIPP: tax relief in (max £60K), tax out (75% taxable). ISA: no tax relief in (£20K), no tax out. SIPP wins for higher-rate taxpayers expecting basic rate in retirement. ISA wins for flexibility.
What's the LSA?
Lump Sum Allowance, £268,275 - replaces the old Lifetime Allowance (LTA) abolished April 2024. Caps total tax-free PCLS across all pensions over your lifetime.
Carry forward unused allowance?
Yes. Use up current year's £60K, then carry forward unused from previous 3 tax years. Useful for one-off windfalls.
Salary sacrifice into SIPP?
Most workplace pensions accept salary sacrifice (saves NI for both you and employer). SIPPs don't natively, but some employers will pay your gross contribution directly via salary sacrifice arrangement.
Inheritance?
SIPP passes to beneficiaries free of IHT (currently). If you die before 75: tax-free withdrawal. After 75: taxed at beneficiary's marginal rate. From April 2027: SIPPs may become subject to IHT (consultation ongoing).
The math of compound growth
Compounding is the engine of every long-term investment plan. The formula for monthly contributions:
FV = PMT x ((1+r)^n - 1) / r
where PMT = monthly contribution, r = monthly return rate, n = months. With a one-time lump sum P at the start: FV += P x (1+r)^n.
Why starting early matters more than contributing more
Saving £500/month from age 25 to 65 (40 years) at 8% reaches ~£1.75M. Same £500/month starting at 35 reaches only ~£745K. The 10 extra years more than DOUBLES the final balance - that's the difference between compounding for 30 vs 40 years.
The first £100K is the hardest
Charlie Munger's observation: getting to £100K is brutal because you depend on contributions, not returns. After £100K, returns start to do more work than your savings. After £1M, your annual return often exceeds your annual contribution.
Tax-advantaged account types by country
| Country | Pre-tax (defer) | After-tax (Roth-style) | Annual limit (2026) |
|---|---|---|---|
| US | 401(k), Traditional IRA, HSA | Roth IRA, Roth 401(k) | £23,500 401(k) / £7,000 IRA / £4,300 HSA |
| UK | Workplace pension, SIPP | ISA (Stocks/Cash/LISA) | £60,000 pension annual / £20,000 ISA |
| Canada | RRSP, FHSA | TFSA | 18% income RRSP / £7,000 TFSA / £8,000 FHSA |
| Australia | Super (concessional) | Super (non-concessional) | AUD 30,000 concessional / AUD 120,000 non-conc |
| India | EPF, NPS, PPF | Equity LTCG (limited) | Rs 1.5L 80C / Rs 50K NPS / Rs 1.5L PPF |
| Singapore | SRS | CPF top-ups | SGD 15,300 SRS (Singaporean) / 35,700 (foreigner) |
| Germany | Riester, Rürup, bAV | Few options | EUR 29,344 Rürup max |
The four investment principles
- Asset allocation > stock picking: 90%+ of long-term return variance comes from your stocks/bonds/cash split, not from which specific stocks. Low-cost index funds beat 80%+ of active managers over 10+ years.
- Costs compound too: a 1% annual fund fee compounds to ~25% of total return over 30 years. Prefer index funds with TER under 0.20%.
- Time in market beats timing: missing the 10 best days in the market drops a 30-year return from ~9% annualized to ~5%. Those days cluster near crashes - selling in fear locks in losses.
- Inflation eats nominal returns: 7% nominal return at 3% inflation is 4% real return. "Safe" cash at 1% loses ~2% real per year. Real returns matter.
Glide path: how allocation should change with age
The classic rule "100 minus your age in stocks" is too conservative for modern lifespans. Updated guidance:
| Age | Equity % | Bonds % | Cash % |
|---|---|---|---|
| 25-35 | 90-100% | 0-10% | 0% |
| 35-45 | 80-90% | 10-20% | 0% |
| 45-55 | 70-80% | 15-25% | 5% |
| 55-65 | 55-70% | 25-35% | 5-10% |
| 65+ (retired) | 40-60% | 30-50% | 10% |
If you retire at 65 and live to 90, your retirement portfolio still has 25-year horizon. Too conservative an allocation runs out of money. Too aggressive risks sequence-of-returns disasters early in retirement.
Frequently asked questions
How much do I need to retire?
The 4% rule: you can withdraw ~4% of your portfolio annually with high confidence of lasting 30+ years. So if you need £50K/year, target £1.25M. The rule was developed for 30-year retirements in the US - for 40+ years (early retirement) use 3-3.5%.
Is the stock market too risky for me?
Over 1-year periods: very volatile, ~30% historical loss possible. Over 10-year periods: 95% positive historically. Over 30-year periods: 100% positive in any rolling US window. Risk depends on time horizon, not the asset class itself.
Should I pay off the mortgage or invest?
Compare your mortgage rate to expected investment return. If mortgage rate is below 5% and your retirement contributions are maxed, investing usually wins long term. Above 7%, the guaranteed return from paying off the mortgage often wins.
How much should I save each month?
Rough target: 15-20% of gross income toward retirement, starting at 25. If you start at 35, you need 25-30%. At 45, 40%+. Saving rate matters more than investment selection for the first 10-15 years.
What's the safest investment?
Short-term government bonds in your home currency. Inflation-linked bonds (TIPS US, ILBI India, index-linked gilts UK) protect against inflation. Bank savings accounts up to insured limits (£250K US FDIC, £85K UK FSCS) are also safe but lose to inflation.
How accurate is the SIPP Calculator (2025/26)?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the SIPP Calculator (2025/26) free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the SIPP Calculator (2025/26) on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the SIPP Calculator (2025/26) work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the SIPP Calculator (2025/26)?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the SIPP Calculator (2025/26)?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another sipp calculator (2025/26) tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.
Real-world scenarios where the SIPP Calculator (2025/26) helps
Day-to-day decisions
Quick estimates without opening a spreadsheet. The SIPP Calculator (2025/26) runs the math instantly so you can compare options, sanity-check assumptions, and move on.
Planning ahead
Build a forward-looking model. Change one variable at a time to see how sensitive the sipp calculator (2025/26) output is to each input. The variable that moves the result most is where you should focus your real-world attention.
Cross-checking advisors
Compare what a professional or quoted source tells you against an independent calculation. Discrepancies are conversations worth having before signing.
Documentation
Capture inputs and outputs at a point in time. Screenshot the result with the date for audit trails, joint decisions, or future reference.
Learning intuition
By varying inputs, you build a sense of how sipp calculator (2025/26) actually behaves. The numerical pattern teaches faster than reading prose.
Sensitivity analysis
Identify which input drives the result. The most-impactful variable is where small improvements pay off most.
Comparing alternatives
Run the same sipp calculator (2025/26) calculation across multiple options and rank them by the dimension you care about (cost, return, speed, risk).
Pre-meeting preparation
Walk into a negotiation, sales call, or strategic discussion with the sipp calculator (2025/26) numbers already in your head. Beats winging it from memory.
What the SIPP Calculator (2025/26) does and does not handle
What it does
- Applies the standard formula widely accepted in sipp calculator (2025/26)-related calculations.
- Updates instantly as you adjust inputs - useful for sensitivity analysis and what-if scenarios.
- Runs entirely in your browser using JavaScript. Your inputs never reach a server.
- Handles common edge cases (zero values, very large numbers, negative inputs where applicable) with sensible defaults or validation messages.
- Works offline once the page is cached. No internet needed for repeat calculations.
- Free, unlimited use. No signup, no rate limits, no paywall.
What it does not handle (and where to go)
- Personal financial advice - the calculation gives you a number, not a recommendation. Speak to a qualified advisor for decisions with significant financial consequences.
- Country-specific rules where local variation is high - the tool uses the most common methodology; some jurisdictions have variations.
- Real-time market data when applicable - most calculations use static reference values. Live market prices are out of scope.
- Auto-filling from external accounts - all inputs are manual. Browser autofill works for repeated entries.
- Saving results across devices - all state lives in this browser session.
Common mistakes and pitfalls
- Using rough estimates as inputs. Garbage in, garbage out. The SIPP Calculator (2025/26) is only as accurate as what you type. Look up exact numbers from your statement, contract, or source document.
- Confusing units. Most fields are labeled (currency, percent, kg, etc.) but read the label before typing. A monthly figure entered into an annual field will be off by 12x.
- Ignoring the assumptions baked into the formula. Every calculator has assumptions (e.g., uniform growth rate, no fees, no taxes). Read the methodology section to understand what's included and what's not.
- Comparing without holding other variables constant. When testing options, change only ONE input at a time. Changing multiple inputs makes it impossible to tell which one drove the result.
- Treating the result as final. The output is a model. The real world adds fees, taxes, timing differences, and exceptions. Use the result as a starting point, not a final answer.
- Misreading rounded display. Most fields display 2 decimal places but compute at full precision. Two inputs that look identical may produce slightly different outputs.
Best practices for accurate results
- Pull exact values from authoritative sources (bank statement, payslip, official rate table, contract) rather than ballparking from memory.
- Match units carefully. Watch for monthly vs annual, gross vs net, percent vs basis points, USD vs INR.
- Run the calculation multiple times with slightly different inputs to see how sensitive the result is.
- Screenshot or note the inputs alongside the output for future reference - results change if rules or rates change.
- Cross-check against a professional source (advisor, accountant, official tool) for any decision with material impact.
- Update annually. Tax rates, contribution limits, and benefit thresholds change yearly. Rerun key calculations every January.