How to use it
- Enter your age, ISA balance, what you add each year, and what you’d withdraw each year once you stop work.
- Set the age your pension or other income starts, and a real growth rate.
- Choose Target age to test a retirement age you have in mind, or Earliest age to solve for it.
- Read the result, then compare the three growth rates on the chart and table.
About
Retiring before your pension can be taken (from 57 or 58, or 68 for the State Pension) means something has to pay for the years in between. For many people that’s an ISA. This finds your ISA apex: the balance your ISA needs to reach on the day you stop work, so that withdrawals carry you exactly to the day your pension starts.
Before the apex your ISA grows with contributions; after it, withdrawals run it down to roughly zero by the end of the bridge. The calculator compares the balance you’re projected to have with the apex you need, and tells you the shortfall or surplus, plus the yearly contribution that would hit your target age.
Everything is in today’s money: the growth rate is a real rate, after inflation and fees (for example, 8% market return minus 3% inflation and fees is about 5% real). Results are shown 1% either side of your rate, because small changes in growth move the answer more than people expect. It’s a model, not financial advice.
This accompanies the article The Road to FIRE: Building the ISA Bridge to 58 and Finding the Apex, which walks through the reasoning and a worked example.
Questions
What is the ISA apex?
The highest point your ISA reaches, on the day you retire. From then on withdrawals bring it down, ideally to about zero just as your pension starts.
Why use a real growth rate?
So every figure is in today’s money. A flat withdrawal in real terms means your spending keeps pace with inflation.
Why do the earliest ages look the same at different growth rates?
Ages are whole years, so small differences can round to the same age. The exact crossover point, shown in months, reveals the difference.