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Last reviewed: 11 October 2026
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Drag events onto the timeline to make your plan. Enter your details on the Inputs page. Compare the three scenarios in the Scenarios section of the Plan page. Manage your account on the Accounts page.
How PlanBox calculates your plan
This page explains how PlanBox calculates your plan. It states the tax year, the tax rates, and the main methods behind your plan.
Money and inflation
PlanBox shows every amount of money at current prices. This is a real-terms amount. A real-terms amount removes the effect of future inflation. A pot of £100,000 keeps the same buying power at every age in your plan.
Tax and National Insurance
PlanBox models the 2026/27 tax year for Income Tax and National Insurance. The table below lists the rates and thresholds it uses. National Insurance stops at State Pension age.
| Rate or threshold | Amount |
|---|---|
| Personal Allowance | £12,570 a year |
| Personal Allowance taper starts at | £100,000 |
| Personal Allowance reaches zero at | £125,140 |
| Basic rate band, on income more than the Personal Allowance | £37,700 at 20% |
| Higher rate | 40% |
| Additional rate, on income more than | £125,140 at 45% |
| National Insurance main rate | 8%, from £12,570 to £50,270 |
| National Insurance rate on earnings more than | £50,270 at 2% |
State Pension
PlanBox models the new State Pension. The full amount is £12,548 a year at State Pension age 67. You need 10 qualifying years for any State Pension, and 35 years for the full amount. Each year you defer it adds 5.8% to the amount. PlanBox models deferral up to 10 years.
PlanBox pays the State Pension from State Pension age. It pays it when you work full-time, when you work part-time, when you take a sabbatical and when you stop work. PlanBox adds the State Pension to your other taxable income for that year and applies Income Tax to the total. It does not apply National Insurance to the State Pension. For a couple, PlanBox applies each State Pension to the personal allowance of that partner. If you set a State Pension deferral, PlanBox pays it from the end of the deferral.
Monte Carlo
PlanBox runs 500 separate futures for your plan, a method called Monte Carlo. It adds your pension pot, your ISA pot, your Lifetime ISA pot and your other investments pot into one total for the fan chart. This total does not decide if your plan survives. Your plan survives if your income and the pots that you can take money from pay your spending. It includes the repayments on your mortgage and on your other debts.
Each pot has its own average return. Your pension pot, your ISA pot and your Lifetime ISA pot use the average return of the scenario, after your fees. Your other investments pot uses the Other return that you set, and it pays no fees. Each year of each future, one random market change from a normal distribution applies to all your pots. Each random market change is independent of every other year and every other future. The 500 futures are not real market history.
Each scenario sets its own average return and its own spread, called sigma. The table below lists the spread for each scenario. The Scenarios section of the Plan page shows one Plan survives figure for each of the three scenarios. Every other Plan survives figure, including the Plan survives tile, uses the scenario that you select. The tile is on the Insights page on a narrow screen, or in the Insights panel on a wide screen.
| Scenario | Spread |
|---|---|
| Pessimistic | 10% |
| Normal | 12% |
| Optimistic | 15% |
How PlanBox spends your pots
In retirement, PlanBox pays your spending from your pots in a fixed order. It takes money from your pension pot first, once you reach your pension access age. It takes money from your ISA pot next. It takes money from your Lifetime ISA pot next, once that pot is unlocked. It takes money from your other investments pot last.
Fees
PlanBox takes adviser fees and platform fees from your ISA pot, your pension pot and your Lifetime ISA pot. It does not take these fees from your other investments pot. A one-off initial fee comes from your ISA pot and your pension pot only.
If you set a fixed adviser fee, these three pots share the fee. Each pot pays a part of the fee. That part is in proportion to the money in the pot. A fee cannot take more money than the pots hold.
Limits of the model
PlanBox does not model every tax rule or every type of pension. The main limits are below.
- Tax on money you take from your pots, and some taxes on investments.
- One type of pension pot only, in addition to the State Pension.
- Simplified tax rules for couples, and one State Pension record for both partners.
- Salary held at its current amount, with no salary growth.
PlanBox does not calculate Inheritance Tax. It flags a large pension pot at retirement, because a pension pot can form part of your estate from 6 April 2027. It also flags a pension pot that is equal to or more than the Lump Sum Allowance of £268,275.
PlanBox projects your plan to age 100 for everyone. This is a planning convention, not a forecast of your lifespan. It gives most people a wide safety margin, but it does not model care costs unless you add them yourself. PlanBox prices its own three care tiers, from £68,000 to £150,000 a year.
Glossary
- Monte Carlo
- A method that runs many possible futures for investment returns and counts the futures in which your plan survives.
- Pot
- Money held in one part of your plan, for example your pension pot or your ISA pot.
- Plan survives
- A future in which your income and the pots that you can take money from pay all of your planned spending. This applies to each year from your retirement age to age 100 in which PlanBox counts no salary or part-time pay for your household. A pension before the age that you can take money from it, or a Lifetime ISA before age 60, does not pay your spending. Your emergency fund does not pay your spending. A plan with no savings survives if your income pays all of your spending.
- Drawdown
- The money PlanBox takes from your pots each year to pay for your spending, in the order above.
- 4% rule
- A rule of thumb that your pots can support yearly spending equal to 4% of their total at retirement.
- p10, p90
- At each age, p10 is the amount that 10% of the 500 futures are equal to or less than. p90 is the amount that 90% of the 500 futures are equal to or less than.
- Sigma
- The spread of the random market changes in each scenario.
- NMPA
- Normal Minimum Pension Age, the earliest age you can access a pension pot. It is 57 from 6 April 2028. The default access age PlanBox uses is 57 for everyone. Set 55 only if your provider confirms a protected pension age of 55, or you start drawing from your pension before 6 April 2028.
- GIA
- General Investment Account (GIA). PlanBox calls this your other investments pot.
- Go-go years
- The early years of retirement, when spending is often higher than in later years.
Questions before you buy
What does PlanBox model?
PlanBox models your income, spending, pension, ISA, Lifetime ISA, other investments, mortgage and State Pension together in one household plan.
Which tax rules does PlanBox use?
PlanBox applies UK Income Tax for the 2026/27 tax year to your salary, State Pension and other income. It applies employee National Insurance to your earnings from work only. It does not tax money you take from your pots.
What does Monte Carlo do here?
PlanBox runs 500 random futures for your pension pot, your ISA pot, your Lifetime ISA pot and your other investments. It reports the share of futures in which your plan survives. It includes the repayments on your mortgage and on your other debts.
Where is your data stored?
PlanBox stores your plan on this device. If you sign in, PlanBox also stores your plan in a secure account so you can reach it from another device.
How do I cancel?
Go to the Accounts page and select Manage subscription. Cancel your subscription on the billing page that opens.
How do I export my plan?
Go to the Settings page and select Export current as JSON.
Contact and disclaimer
PlanBox is made for UK households. It is not financial advice. Talk to a qualified financial adviser before you make a decision based on this plan.
Email us at hello@planbox-app.uk.