Distilling the Number — How My Financial Advisor Got to 47

I sat across from my financial advisor and heard the number: 47. That’s when I could retire, they said. I felt a small wave of relief getting confirmation that I don’t need to work until standard retirement age, but I didn’t really understand how they got to that number.

I decided building a calculator would give me a more hands-on, deeper understanding of how to calculate my realistic retirement age — the levers involved, what to adjust, and how it all comes together. This is what I learned along the way.

If you’d like to calculate your target retirement age, grab your latest W-2 and have a rough estimate of your current net worth and annual spending and enter your details below.

Where do I find these numbers?

You only need three things: your W-2, a rough net worth, and a rough idea of what you spend.

Net worth — add up everything in your investment and savings accounts. Checking, savings, brokerage, 401(k), IRA, HSA. Don’t count your house or car. If you’re not sure, just log into each account and add up the totals. A rough number is fine.

Monthly rent or mortgage — what you pay for housing right now. This is broken out separately because housing is usually your biggest expense, and it’s the one most likely to change dramatically — switching from renting to owning, moving cities, or eventually paying off a mortgage.

Other annual spending — everything that isn’t housing. Groceries, restaurants, travel, subscriptions, insurance, all of it. Look at your bank and credit card statements for a few months and multiply. It doesn’t need to be exact.

The W-2 fields — the rest comes straight from your W-2. Here’s where to find each one:

• Gross salary — Box 1
• Federal + state taxes — Box 2 + Box 17
• Social Security + Medicare — Box 4 + Box 6 (these are the payroll taxes, sometimes called FICA)
• 401(k) — Box 12, Code D
• HSA — Box 12, Code W (if you don’t have one, just leave it at zero)

What the snapshot tells you

Before you run the full projection, the calculator shows you three numbers on the right side. These update instantly as you type.

Net take-home is what actually lands in your bank account. Salary minus all the taxes and pre-tax deductions.

Total saved per year is everything going toward your future — what’s left after spending, plus your 401(k) and HSA contributions.

Savings rate is the one that matters most. It’s your total savings divided by your after-tax income. This single number tells you more about your trajectory than your salary does.

Life changes

Most retirement calculators treat your life as a straight line — same spending, same income, every year until you stop working. Real life isn’t like that.

Housing changes. If you’re renting now but plan to buy a home, your housing cost might jump from $2,100/month to $4,000/month. That extra $22,800 a year in spending means $22,800 less saved — and that compounds over decades. Enter the age you expect the change and the new monthly cost, and the calculator adjusts both your savings during working years and your spending in retirement.

Income phases. Maybe you don’t want to go from full-time to fully retired overnight. A lot of people downshift — consulting part-time, freelancing, or working on something they actually enjoy for less money. Click “Add income phase” and enter the age range and annual income. The calculator treats that income as money your portfolio doesn’t have to cover during those years, in both the deterministic and Monte Carlo projections.

You can combine these. For example: housing jumps at 38 when you buy a place, you leave full-time work at 45 but consult for $40K/year until 55, then fully retire. The calculator handles all of it.

How the math actually works

I built this calculator because I wanted to understand the math my advisor was using — not just trust it. Here’s what’s happening under the hood, in plain English.

The calculator asks one question for each retirement age: if I stopped working at this age, would my money last until 95?

It answers that in two parts.

Part 1: What you’ll have

The calculator walks through each year from now until retirement. Each year, your existing portfolio grows by the expected return (7% by default), then your savings for that year get added on top.

Your savings in any given year are: take-home pay minus spending, plus pre-tax contributions (401k, HSA). The salary side grows a little each year (2% by default, reflecting modest raises). The spending side tracks your housing and other expenses separately — so if your housing cost changes at a specific age, the calculator adjusts your savings accordingly.

The total at the end of the accumulation phase is your Total Assets at each retirement age.

Part 2: What you’ll need

This is the part that surprised me. You might think it’s just “my annual spending times the number of years I’ll live.” It’s not.

The real question is: what lump sum do I need on day one of retirement so that I can withdraw what I need each year, adjusted for inflation, and never run out?

That’s a harder question, because your spending gets more expensive every year. At 3% inflation, $50K today becomes about $69K in eleven years. And you need to fund that rising spending for potentially 50 years. The math accounts for the fact that your remaining portfolio keeps growing while you’re withdrawing from it — so it’s a balance between what’s going out and what’s still compounding.

On top of living expenses, the calculator includes a few things most people don’t think about:

Healthcare before Medicare. If you retire before 65, you need to cover your own health insurance. The default is $2,000/year, which is low — I’m fortunate to be on my spouse’s plan. If you’d be buying ACA marketplace coverage, this could be $10–20K a year.

Long-term care. This is the uncomfortable one. The final years of life often involve expensive care — home aides, assisted living, memory care. The calculator assumes about $128K/year for the last two years, with medical inflation at 4%. It’s hard to think about, but leaving it out makes the math falsely optimistic.

Social Security. This one works in your favor — it gets subtracted. Once you hit 67, Social Security starts covering part of your spending, so your portfolio doesn’t have to. The default is $1,800/month, which is conservative for someone who stops working early. You can check your actual estimate at ssa.gov/myaccount.

Part 3: Does it actually work?

This is where it gets interesting.

Everything above assumes the market returns exactly 7% while you’re working and exactly 5% while you’re retired, every single year. That never happens. Some years the market is up 25%. Some years it’s down 15%. The order those years happen in matters enormously — a crash right after you retire is far more damaging than one twenty years in.

So the calculator runs what’s called a Monte Carlo simulation. It plays out your entire financial life 2,000 times, each with a different random sequence of market returns. Some of those futures are great. Some are brutal. The percentage shown in the MC Success column is how many of those 2,000 simulated lives made it to 95 without running out of money.

90% is the threshold. If 9 out of 10 randomly generated futures survive, most financial planners consider that safe. It doesn’t mean there’s no risk — it means you’ve accounted for a lot of bad luck and still come out okay.

That’s the column I trust most.

The levers underneath

Click “Adjust assumptions” in the calculator to see what’s driving the numbers. You probably don’t need to change these, but knowing what they are helps you understand what you’re really betting on.

Investment returns — 7% while working, 5% in retirement. The difference reflects shifting from aggressive investments to something more conservative once you’re living off the money. Both are rough historical averages, not guarantees.

Inflation at 3% — things get more expensive every year. The Fed targets 2%, so 3% is a bit of a buffer. It sounds small, but over 50 years, 3% inflation turns a $50K lifestyle into a $219K one.

Life expectancy at 95 — nobody likes thinking about this, but planning to 95 means you’re unlikely to outlive your money. If your family tends to live longer, bump it up.

Social Security at $1,800/month — a conservative estimate for someone retiring early with years of zero earnings on their record. Your actual number from ssa.gov/myaccount will be more accurate.

Healthcare at $2,000/year — only applies before Medicare at 65. If you’d be buying your own coverage, $15–20K/year is more realistic.

Long-term care at $128,000/year — based on national averages for facility care. Medical costs inflate faster than everything else (4% vs. 3%), which is why this number can look startlingly large decades out.

MC simulations at 2,000 — how many random futures the calculator plays out. More runs give a smoother result but take longer. 2,000 is plenty.

What the number means to me

When my advisor said 47, it felt good but abstract — a number I’d been handed, not one I understood. Building this calculator was my way of actually getting there.

The uncertainty I carry about job security doesn’t disappear when the math lines up. But it shrinks. It becomes something I can see clearly rather than something lurking in the background.

What I can see clearly is this: ten more years is enough. Enough to build something that doesn’t require me to keep going indefinitely. Enough to arrive somewhere where my time is mine — to spend on work I actually chose, in a life I actually designed.

That’s what the number means to me. Not a finish line, but a slow burn. Steady, patient, built to last. Go where it’s warm.