Safe Withdrawal Rate (SWR) Tester Calculator

What does the Safe Withdrawal Rate (SWR) Stress Tester calculator do?

The Safe Withdrawal Rate Stress Tester lets you see how long your retirement pot is likely to last based on your spending needs. It runs thousands of simulated market scenarios using Monte Carlo analysis and UK/Global portfolio assumptions to estimate the probability that your money will last through retirement. Your safe withdrawal rate is calculated automatically based on your chosen spending and total pot size.

How the Calculator Works?

You enter your full retirement pot across ISA, SIPP, GIA, BTL proceeds and cash, along with your annual spending target. The calculator then runs thousands of Monte Carlo simulations using return patterns based on UK and Global historical data. Each simulation models how markets may rise or fall each year and tests whether your pot survives over your chosen retirement horizon. The tool reports a success rate and calculates the implied withdrawal rate based on your spending and pot size.

Step One: Enter Your Pot and Spending

Add your total retirement pot (ISA, SIPP, GIA, BTL and cash) and set your annual spending needs. This determines the size of withdrawals tested during the simulation.

Step Two: Choose Portfolio and Retirement Assumptions

Select UK-only or Global portfolio assumptions, set your retirement length and adjust volatility or return assumptions if required.

Step Three: Review Success Rates and Your Safe Withdrawal Rate

The tool runs thousands of simulations and shows the probability that your pot lasts your full retirement. It also calculates the implied withdrawal rate based on your spending relative to your pot size.

Safe Withdrawal Rate Stress Tester

Stress test your retirement spending plan. Enter your annual spending needs and see how long your pot (ISA, SIPP, GIA, BTL, and cash) is likely to last across thousands of simulated market scenarios. Uses Monte Carlo simulation with UK and Global portfolio assumptions to show probability of success. The withdrawal rate is calculated as an output based on your spending and pot size.

Personal details & spending

Current age

How old are you now?

Retirement start age

Age when you start drawing from accessible pots (ISA, GIA, cash). SIPP accessible from age 57.

Model to age

How far do you want to stress test to?

Annual spending in retirement (today’s £)

Target annual spending in real (inflation-adjusted) terms. State Pension and DB pensions reduce required withdrawals from your pot when they start.

State Pension (annual, today’s £)

Annual State Pension amount (currently £11,502 for full pension). Starts at age 67.

I have a Defined Benefit (DB) pension

Current investment values

Enter your current investment values. The calculator will model growth between now and retirement age.

SIPP / Pension (£)

Current defined contribution pension value.

ISA (£)

Stocks & Shares ISA value.

Cash savings (£)

Cash in savings accounts.

Other investments (£)

General investment accounts, etc.

Buy-to-Let property (if applicable)

Property value (£)

Total property value.

Annual rental income (£)

Gross annual rental income.

Outstanding mortgage (£)

Remaining mortgage balance.

Mortgage rate (%)

Annual interest rate on BTL mortgage.

Void rate (%)

% of rent lost to voids (empty periods).

Repairs/maintenance (%)

% of rent for repairs and maintenance.

Portfolio allocation & assumptions

Portfolio region (for SIPP, ISA & GIA)

UK-focused (UK equities & gilts) Global diversified (e.g. Vanguard Global All Cap)

Equity allocation (%)

For SIPP, ISA and GIA investments.

Bond allocation (%)

For SIPP, ISA and GIA investments.

Annual fees (%)

Fund OCF + platform fees for SIPP/ISA/GIA.

Simulation settings

How Monte Carlo simulation works:

The calculator runs thousands of simulated retirement scenarios, each with different market returns. Each simulation randomly generates investment returns based on historical UK/Global market patterns (mean returns and volatility). This creates many possible future paths for your portfolio. The results show percentiles (5th, 50th, 95th) – meaning 95% of simulations performed better than the 5th percentile, and 50% performed better than the median. More simulations = more accurate results but slower calculation.

Number of simulations

More simulations = smoother, more accurate results but slower. Recommended: 2000+.

Confidence level (%)

Used for “survival age” calculation. 95% means your pot survives to that age in 95% of simulations.

Results

We model your retirement pot in real (inflation-adjusted) terms, year by year, across many simulated market paths, to estimate how likely it is to survive to different ages. The calculator models: pre-retirement growth from your current age to retirement, pension access restrictions (SIPP from age 55), and State Pension income from age 67.

How it works: Each simulation generates random market returns based on historical UK/Global patterns. Returns are applied each year (accounting for market growth), then withdrawals are made. The 5th percentile represents worst-case scenarios with poor returns or sequence risk (market crashes early when you’re withdrawing). The median shows typical outcomes. All scenarios include full market growth modeling – the difference is the sequence and magnitude of returns.

Initial withdrawal rate (at retirement) – Annual spending ÷ Pot at retirement

95% survival age –

Success to age 90 –

Success to age 95 –

Success to age 100 –

Portfolio value over time (percentiles)

5th percentile (worst case): Only 5% of simulations performed worse. Shows scenarios with poor market returns or sequence risk (market crashes early when withdrawing). Median (typical): 50% better, 50% worse – the most likely outcome. 95th percentile (best case): Only 5% performed better – strong market returns. All scenarios model full market growth each year – returns are applied before withdrawals. The gap between 5th and median reflects sequence risk and market volatility.

Success probability by age

Percentage of simulations where your pot remains above zero at each age. A declining line indicates increasing risk of depletion.

Year-by-year view (median vs worst-case scenario)

The 5th percentile shows the worst-case scenario where only 5% of simulations performed worse. This accounts for market growth but represents poor sequence of returns (e.g., market crashes early in retirement when you’re withdrawing).

Age	Year	Median pot (£)	5th percentile pot (£)

This tool uses simulated real returns and cannot predict the future. It’s for education and planning only and is not personal financial advice.

Disclaimer: This calculator provides illustrative results only and does not constitute financial advice. Monte Carlo simulations use historical assumptions that may not reflect future market conditions. Seek guidance from a qualified financial adviser before making retirement income decisions.

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What is the Safe Withdrawal Rate (SWR) Stress Tester?

It is a Monte Carlo based tool that tests whether your retirement pot can support your spending across thousands of simulated market paths and calculates the withdrawal rate implied by your plan.

What does this calculator estimate?

It estimates the likelihood that your retirement pot will last your full retirement, given your annual spending needs. It also calculates the withdrawal rate your spending represents.

How does the Monte Carlo simulation work?

The tool runs thousands of simulated market paths using expected returns and volatility based on UK and Global data. Each path shows a different sequence of returns, illustrating how variable markets affect retirement sustainability.

What information do I need?

You will need your total retirement pot (ISA, SIPP, GIA, BTL proceeds and cash), your annual spending requirement, portfolio preference (UK or Global) and your planned retirement length.

Does the calculator include taxes?

It focuses on net pot values and spending. If you want to include tax, reduce your pot or increase your annual spending to reflect the tax you expect to pay.

Does this tool model investment fees?

Yes. Please set these within the Portfolio allocation & assumptions section.

What is the “safe withdrawal rate” in this tool?

It is the withdrawal rate implied by your pot size and annual spending. The tool does not ask you to choose a rate; instead, it calculates it based on your inputs and tests whether it is sustainable.

Why does the success rate matter?

A higher success rate means your plan is more likely to survive market downturns. Many retirees look for success rates of 85 per cent or above, but the right level depends on your comfort with risk and flexibility in spending. For example, if you choose to retire from traditional work early, you may have more of a risk tolerance as there’s always an option to take on additional work, especially if age is on your side.

What’s the difference between UK and Global portfolio modes?

: UK uses domestic equities and bonds

: Global uses diversified global index assumptions

Global tends to offer more diversification and smoother outcomes, but you can test both.

Is my information stored?

No. All calculations run locally in your browser and are not saved or transmitted.

How accurate are the results?

They are scenario-based estimates. They help you understand risk and resilience, but they cannot predict future markets. Use multiple assumptions to build a robust plan.

Retirement Calculators

Safe Withdrawal Rate (SWR) Stress Tester Calculator (UK Specific)