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MaxiFi vs Delphina: FIRE Tracking

You have £340,000 in your ISA and SIPP, you save £2,800 a month, and you want to know whether you can stop work at 52. MaxiFi will give you a probability. Delphina will give you a date. Here is which is more useful.

How MaxiFi approaches FIRE

MaxiFi runs Monte Carlo simulations. You enter your portfolio, your planned retirement date, your expected spending, and the tool runs the scenario thousands of times against historical and forward-looking asset returns. The output is a probability: "you have a 78% chance of not running out of money by age 95."

This is sophisticated. The problem is that you cannot act on a probability easily. If the answer is 78%, do you save more, retire later, or accept the risk? MaxiFi gives you the modelling but not the decision. It also assumes US asset returns, US inflation paths and US Social Security, which makes the output less reliable for a UK household.

How Delphina approaches FIRE

Delphina uses the 4% safe withdrawal rule, expressed in UK terms. Your FIRE number is 25 times your real annual spending. A household spending £42,000 a year needs £1,050,000 invested before the portfolio can sustain that withdrawal indefinitely. Delphina also reads your actual spending from your bank, so the £42,000 is not a guess you typed in once, it is what you actually spent last year.

Then Delphina projects forward month by month using your real savings rate and expected returns, and gives you a date. "At your current pace, you reach £1,050,000 in March 2034, age 51." You can adjust your retirement age, your monthly contribution, or your expected return and see the date shift immediately. It is less sophisticated than Monte Carlo, but the answer is one you can act on this week.

The real difference

MaxiFi answers "what is the probability I succeed?". Delphina answers "when do I succeed, and what changes the date?". For most UK households thinking about FIRE, the second question is the one that drives decisions. Knowing you have an 87% chance of success at age 52 versus 92% at age 55 is interesting. Knowing that putting an extra £400 a month into your SIPP brings the date forward by 14 months is actionable.

If you want both, Delphina runs Monte Carlo on the retirement projection too. The output is the FIRE number as a single figure, which is what most people actually need.

Who should pick which

Pick MaxiFi if

-You want a probability-based answer for a US-based portfolio.
-You are comfortable interpreting Monte Carlo outputs and managing sequence-of-returns risk yourself.
-You want US-specific modelling of Social Security timing and Medicare premiums.

Pick Delphina if

-You are a UK household and want a FIRE number built on your actual spending.
-You want a specific date and a clear lever (save more, retire later, spend less) to move it.
-You want the projection to update automatically as your savings rate changes.

One thing to do this month

If FIRE is the plan, write down your real annual spending for the last 12 months from your bank statements, then multiply by 25. That is your number, today, with no app. Whatever it is, you have a starting point. Connect Delphina this week to find the date.