I've found that most retirement planning conversations happen at too high a level of abstraction to be useful — the real answer requires running numbers that are specific to your actual situation.
Retirement planning has a reputation for being complicated. The core question is actually simple: do you have enough money to stop working and cover your costs for the rest of your life? The complexity comes from estimating how long that life will be, how markets will perform, and what your costs will look like. Here is how to get to a defensible number.
Retirement Planning Basics
The fundamental maths: you need a pot of money large enough that a sustainable annual withdrawal covers your living expenses. Everything else — tax wrappers, asset allocation, drawdown strategies — is detail layered on top of this basic structure.
Start with three questions. What will you spend each year in retirement? What income will you receive from non-portfolio sources — State Pension, defined benefit pension, rental income? And how long might retirement last?
Annual spending minus non-portfolio income gives you the annual withdrawal required from your investment portfolio. The portfolio target is that withdrawal amount divided by your chosen withdrawal rate. At a 4% withdrawal rate, divide by 0.04 — equivalently, multiply by 25. At 3.5%, multiply by approximately 28.6.
Example: you want to spend £40,000 per year. You expect £9,500 per year from the State Pension. Your portfolio needs to produce £30,500 per year. At 4%: £30,500 ÷ 0.04 = £762,500. At 3.5%: approximately £871,000. Use the Net Worth Target Calculator to run this with your specific numbers, including current net worth and how long you have until your target retirement age.
Safe Withdrawal Rates
The 4% rule comes from the Trinity Study, which analysed historical US market data across 30-year retirement periods and found that a 4% initial withdrawal rate — adjusted annually for inflation — survived virtually all historical scenarios including the Great Depression and the 1970s stagflation period.
This is a useful benchmark, not a guarantee. Key limitations to understand:
It is based on historical data. Future returns may be lower, particularly from current valuations. Several analysts now suggest 3% to 3.5% as a more prudent rate for people retiring today.
It was designed for 30-year retirements. Retire at 55 with a 40-year horizon and the 4% rule has less historical support. A 3.5% or 3.25% rate is more appropriate for early retirees.
Sequence of returns matters. A large market drop in the first three to five years of retirement is disproportionately damaging because you are selling assets at low prices to fund withdrawals. Having one to two years of spending in cash or short-term bonds provides a buffer that avoids forced selling during downturns.
Lifestyle Factors
The retirement spending estimate is the input that most people get wrong, in both directions. Here are the adjustments most commonly overlooked:
Costs that disappear: Mortgage payments (if cleared before retirement), commuting costs, pension contributions, work clothing and related expenses, lunch costs from working. These can reduce required spending by £5,000 to £15,000 per year compared to working life.
Costs that increase: Healthcare and dental costs rise with age, particularly private cover. Leisure and travel spending often peaks in the early years of retirement when health is good and freedom is new. Home maintenance costs rise on an ageing property. Heating costs increase with time spent at home.
Phased retirement spending: Many retirees find spending is higher in the first 10 to 15 years (the active phase), then reduces in the middle years, then potentially rises again in late retirement due to care costs. A flat annual spending estimate applied across 30 or 40 years may overstate or understate at different points. Building this into your planning — rather than assuming constant spending — produces a more realistic picture.
A Worked Example
Sarah is 45, plans to retire at 62, and wants to spend £3,200 per month (£38,400 per year) in retirement. She expects £9,500 from the State Pension from age 67 and has a deferred workplace pension worth £6,000 per year from 65. Her net worth currently stands at £180,000.
From 62 to 65: needs £38,400/year from her portfolio. From 65 to 67: needs £32,400/year (pension starts). From 67 onwards: needs £22,900/year (State Pension also starts). The portfolio target is approximately £700,000 to cover these phases with a 3.5% withdrawal rate applied to the highest-need period.
At 6% average annual return with her current £180,000 invested, she needs to save approximately £1,900 per month over 17 years to reach £700,000. More than she currently saves, but a specific and achievable target rather than an abstract aspiration.
What to do next
Use the ideas above as a starting point — then connect them to your own numbers and related guides on Calc It Anything.
- Read the personal finance and money management guide for the wider cluster.
- Compare with The Cost of Waiting to Save: How Delays Destroy Wealth.
- Compare with Why Lifestyle Inflation Sneaks Up on Almost Everyone.
- Run the relevant calculator on this site with your own inputs before making a decision.
Related reading
- personal finance and money management guide
- The Cost of Waiting to Save: How Delays Destroy Wealth
- Why Lifestyle Inflation Sneaks Up on Almost Everyone
- Why Your Pay Rise Feels Smaller Than Expected
- Complete Budgeting, Saving & Personal Money Management Guide
- Complete Compound Interest, Investing & Wealth Building Guide
For official UK context, see MoneyHelper UK.
Frequently asked questions
Does lifestyle inflation always follow a pay rise?
Not inevitably, but it is the default unless you decide allocations before the new salary lands. Automating savings and fixed goals on payday reduces drift into upgraded spending.
How much does starting to invest late actually cost?
It depends on monthly amount, return assumption, and years left. The gap grows non-linearly because early contributions compound longer — run your age and contribution in a compound interest calculator rather than guessing.
What is a sensible first step after reading this?
Pick one number to model — retirement age, savings rate, or debt payoff — in the relevant calculator, then adjust one habit for the next pay cycle. Small consistent moves beat perfect plans you never start.