Scenarios
Help & FAQ

How Scenarios works

Everything you need to know about the simulation engine, UK tax modelling, portfolio assumptions, and how to interpret your results.

Methodology

We run 1,000 independent simulations of your financial future. Each simulation generates a unique sequence of investment returns, inflation rates, and market conditions year by year from now until your chosen end age. At each year, the engine applies your contributions, withdrawals, tax obligations, and fees. The results are then ranked to produce percentile bands — the median (50th percentile) is the "middle" outcome, while the 10th and 90th percentiles show the range of plausible scenarios. This approach captures the uncertainty inherent in long-term financial planning far better than a single "average return" projection.
Each asset class (global equities, UK equities, bonds, property, gold, cash) has an expected return and volatility based on widely-used long-run assumptions for UK investors. Returns are generated using a log-normal model with a full correlation matrix — so when equities fall, bonds don't necessarily fall by the same amount. The Cholesky decomposition of the correlation matrix ensures realistic diversification behaviour across your portfolio.
We use a 7×7 correlation matrix calibrated to post-2000 market regimes. Key relationships include: global and UK equities are highly correlated (0.82), bonds have low or slightly negative correlation with equities (0.05–0.10), and gold provides genuine diversification (0.05 correlation with equities). These capture the reality that diversified portfolios are less volatile than individual asset classes — the "free lunch" of diversification.
Inflation is modelled stochastically — it varies each year rather than being fixed. You set a mean inflation rate (default 2.5%) and a standard deviation (default 2%). For couples, both partners experience the same inflation and investment return paths in each simulation, reflecting the reality that you share an economy. The "Real" view in the dashboard shows all values adjusted back to today's purchasing power using each simulation's actual inflation path.
The tax engine implements 2026/27 HMRC rules including: income tax bands (both rUK and Scottish with all 6 bands), the personal allowance taper above £100,000 (60% effective rate trap), capital gains tax with cost basis tracking and CGT on disposal only (£3,000 exempt, 18%/24% split across bands), dividend tax on GIA equity holdings (£500 allowance, 10.75%/35.75%/41.35%), savings income tax with Personal Savings Allowance (£1,000/£500/£0) and £5,000 starting rate for savings, pension annual allowance (£60,000) and MPAA (£10,000) triggered on first flexible access, pension tax relief (net-to-gross conversion), ISA allowance (£20,000), lump sum allowance (£268,275), state pension triple lock (CPI + 0.5%), rental income expense ratio, and marriage allowance (£252/yr) for eligible couples. Tax bands can optionally inflate with your chosen inflation rate to model fiscal drag.
In retirement, the engine draws income first from guaranteed sources (state pension with triple lock, DB pensions, annuities, rental net of expenses), then applies a tax-optimised withdrawal strategy across your accounts. Each year it takes any available PCLS or UFPLS tax-free cash first, then fills your remaining Personal Allowance with pension income (taxed at 0%), then draws from ISAs (completely tax-free), then further pension at marginal rates, then GIA (CGT on disposal based on cost basis tracking), and finally cash. For couples, both partners draw independently so both Personal Allowances are used every year. You can switch to a custom drawdown order in the Withdrawals tab — including grouping sources at the same priority level so they're drawn proportionally by balance. PCLS vs UFPLS and LSA tracking are also configured there.

Getting Started

At minimum you need your date of birth, target retirement age, current pension and ISA values, approximate contribution amounts, and your expected annual spending in retirement (in today's money, after tax). You can find your pension value by logging into your provider's website or checking your annual statement. If you're unsure of your provider, ask your employer's HR team. Everything else is optional — you can add detail later.
The onboarding wizard takes around five minutes for a single person with a couple of accounts. A couple with multiple pensions, ISAs, and properties might take 10–15 minutes. You can always go back and edit your details from the dashboard sidebar afterwards.
Both. In the setup wizard you choose "Individual" or "Couple". Couple mode models both partners independently — each with their own accounts, pensions, and tax situation — then combines the results into a household view. It also models shared inflation and investment returns so both partners experience the same economic and market conditions in each simulation. Couple mode requires the Duo plan.
The Free plan gives you the core projection chart and personalised insights — enough to see whether your plan is broadly on track. You get one saved plan. Solo (£72/year) unlocks the full tax engine, interactive sidebar sliders, cashflow breakdown, scenario comparison, withdrawal strategy tools, retirement safety analysis, and CSV exports — still one saved plan. Duo (£120/year) adds couple modelling with a combined household plan confidence, shared market conditions, marriage allowance, and two saved plans. See the pricing page for a full feature comparison table.

Accounts & Portfolios

Workplace pensions, SIPPs (self-invested personal pensions), stocks & shares ISAs, cash ISAs (modelled as 100% cash allocation), and General Investment Accounts (GIAs). Each has its own tax treatment, contribution limits, and withdrawal rules that the engine handles automatically.
Each account is linked to a portfolio — a percentage split across seven asset classes (global equities, UK equities, bonds, property, gold, cash, other). You can choose from templates (Aggressive, Balanced, Cautious, etc.) or create custom allocations. The portfolio determines the expected return and volatility of that account. Allocations must sum to 100%.
The fee percentage you enter represents your total annual platform and fund charges (e.g. 0.6% for a typical workplace pension). Fees are deducted from each account's value annually in the simulation. The dashboard shows total fees paid across all accounts over the plan's lifetime — this can be a surprisingly large number and is worth exploring with the fee adjustment slider.
You enter your personal contribution and your employer's contribution separately. Both are added to your pension pot each year before retirement. The engine models auto-enrolment style contributions (where both you and your employer pay in monthly) and lets you adjust either independently in the dashboard sliders.
The engine caps ISA contributions at £20,000 per year (the 2026/27 allowance). If your entered contribution would exceed this, the simulation automatically caps it. A warning appears in the sidebar when this happens. If you have an APS (Additional Permitted Subscription) allowance from a deceased spouse, you can configure this per account.
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Tax & Pensions

Pension contributions receive tax relief at your marginal rate. The engine doesn't explicitly add the relief as a separate line — instead, your contributions are entered gross (the amount that actually lands in your pension pot, including relief). If you contribute £800 net, that's £1,000 gross for a basic-rate taxpayer. Enter the gross figure. Higher-rate taxpayers get additional relief via self-assessment, which is reflected in the effective contribution amount.
For income above £100,000, you lose £1 of personal allowance for every £2 of income. This creates an effective 60% marginal tax rate between £100,000 and £125,140. The engine models this precisely — it's one of the most important tax traps for higher earners and can significantly affect withdrawal strategies in retirement.
The NMPA is the earliest age you can access your private pension without special circumstances. It's currently 55 but rises to 57 on 6 April 2028 for anyone born on or after 6 April 1973. The engine calculates your NMPA from your date of birth and prevents pension withdrawals before that age in the simulation.
The simulation supports two pension withdrawal methods, both drawing from your Lump Sum Allowance (LSA, £268,275 for 2026/27):

PCLS (Pension Commencement Lump Sum) — the tax-free allowance is drawn first. Once exhausted, all further withdrawals are fully taxable at your marginal rate. This front-loads the tax relief.

UFPLS (Uncrystallised Funds Pension Lump Sum) — each withdrawal is split 25% tax-free / 75% taxable, until the LSA is used up. This spreads the relief across every withdrawal.

You can switch between these in the Withdrawals tab, and enter any LSA you've already used from previous crystallisation events. The engine tracks your remaining allowance across all pension accounts and across the full simulation timeline.
Yes. Toggle "Scottish tax rates" in the assumptions section. Scotland has six income tax bands (Starter 19%, Basic 20%, Intermediate 21%, Higher 42%, Advanced 45%, Top 48%) compared to rUK's three. The engine applies the correct band structure including the PA taper interaction with Scottish rates.

Interpreting Results

It's the percentage of simulations where your money lasts until your chosen end age without running out. A 90% probability means that in 900 of 1,000 simulations, your portfolio funded your spending for the entire plan. Remember this is a modelling tool, not a guarantee — real life involves adjustments that the model cannot anticipate.
The fan chart shows how your total wealth might evolve over time. The solid line is the median (50th percentile) — half of simulations end above it, half below. The shaded bands show the 10th–90th percentile range, representing the spread of plausible outcomes. Wider bands mean more uncertainty, which is normal for longer time horizons and higher-equity portfolios.
"Nominal" shows future pound amounts as they'll appear on your statement. "Real" adjusts everything back to today's purchasing power — what those future pounds will actually buy. Real values are generally more useful for planning because £500,000 in 30 years won't buy what £500,000 buys today. The toggle is in the dashboard header.
The cashflow chart has two views. Basic shows coloured stacked bars representing each income source (state pension, private pension, ISA, GIA, etc.) with a solid spending-need line overlaid — if the bars reach or exceed the line, your spending is fully funded that year. In-Depth shows the full picture with income above the axis and spending below, plus a dashed running-balance line. Both views default to real terms (today's pounds) so spending appears flat — switch to nominal to see the "ladder" effect as spending rises with inflation over time.
The Insights tab analyses your simulation results and highlights key findings — like whether your plan is robust, where the biggest risks are, how fees affect your outcome, and whether one partner in a couple is more vulnerable than the other. These are generated algorithmically from the simulation data, not by an external AI service.

Privacy & Data

Your plan data is stored securely in your account and syncs across your devices when you're signed in. Data is encrypted in transit and at rest. We will never sell or share your financial information with third parties. You can export individual plans as PDF or CSV from the dashboard, or download all your data in machine-readable JSON from the Account & Billing page (as required by UK GDPR). You can delete your account and all associated data at any time.
No. Scenarios is an educational modelling tool. It does not provide personal financial advice, recommend specific investments, or tell you what to do. The projections are based on the inputs you provide and long-run statistical assumptions — they are not predictions. For personalised advice, consult a qualified financial adviser regulated by the FCA.
Yes. You can delete individual plans from the My Plans tab, or delete your entire account and all associated data from the Account & Billing tab. Deletion is permanent and cannot be undone. If you'd like to keep a copy before deleting, use the export feature first.
Go to My Account → Account & Billing and click "Manage on Stripe". From there you can cancel auto-renewal. Your access to paid features continues until the end of your current billing period, and no further payments are taken. Your account then reverts to the Free tier — your saved plans are kept, but paid-only features become inaccessible.
Paid subscriptions are non-refundable, but you can cancel anytime with no fees or lock-in — your access continues until the end of your billing period. For exceptional circumstances, contact support@scenarios.uk.

General

Scenarios is built and maintained by a solo developer based in the UK. It was created to give everyday investors access to the kind of financial modelling tools that were previously only available to professional advisers.

Still have questions?

Drop us a line at support@scenarios.uk or try the app — setup takes five minutes and the free plan gives you a full projection instantly.

Scenarios
UK Household Financial Modelling
Tax year 2026/27 — For educational purposes only
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© 2026 Scenarios Software Ltd. Not regulated financial advice.
Scenarios is a trading name of Scenarios Software Ltd. Registered in England and Wales. Company No. 17046348. ICO registration: ZC115276.
Registered office: 1 Lievesley Grove, Nottingham, NG4 4LW