How to Calculate Your Retirement Number If You Plan to Work Part-Time

The standard retirement number — the portfolio balance you need to never work again — assumes a hard stop. You work full-time until a specific age, then you stop completely and your portfolio covers everything from that point forward.

A lot of people do not actually want that. They want to leave their main career at 55 or 58, pick up some consulting work or a part-time job they enjoy, and ease into full retirement at 65 or whenever Social Security kicks in. They want the freedom to stop the demanding work without necessarily stopping all work.

This is semi-retirement, and it is increasingly common in the FIRE community and among people approaching traditional retirement age. The problem is that most retirement calculators cannot model it. You get one retirement date and one income stream. There is no way to say "I earn $40,000 per year from ages 55 to 63, then nothing after that." If early retirement before 59½ is part of the plan, the article on bridging the gap before 59½ covers the account access constraints during that window.

That gap matters, because part-time income in your early retirement years changes your number significantly — often by hundreds of thousands of dollars.

Why Part-Time Income Has an Outsized Effect

The years immediately after you leave full-time work are the most expensive years for your portfolio. You are drawing on it before Social Security starts, before any pension kicks in, and at a point when your balance may not yet be at its peak. Every year you cover some or all of your living expenses with earned income is a year your portfolio does not need to support you.

More importantly, those are years your existing portfolio continues compounding. A portfolio that does not need to make withdrawals for seven years grows significantly more than one that starts distributing immediately.

Take a simple example. You leave your main career at 57 with $900,000 saved. You need $60,000 per year to live. Option A: your portfolio covers all of it from day one. Option B: you work part-time and earn $35,000 per year from 57 to 64, so your portfolio only needs to cover $25,000 per year during that window.

In Option A, you are drawing $60,000 per year from a $900,000 portfolio. In Option B, you are drawing $25,000 per year from the same portfolio — and it keeps growing on the rest. By 65, the Option B portfolio is substantially larger. The part-time income did not just cover expenses during those years. It preserved compounding that compounds again for the rest of your retirement.

The Variables That Actually Drive the Model

To calculate your retirement number with part-time income, you need to capture a few things that standard calculators ignore.

Start age of the income. Part-time work that begins at 55 and runs to 63 is a very different input than consulting income that starts at 60 and ends at 65. The earlier it starts, the more compounding it preserves.

End age of the income. Most part-time retirement plans have a horizon — you are not going to be bartending at 80. The model needs to know when the income stops so it can correctly calculate what the portfolio needs to cover from that point forward.

Whether the income adjusts for inflation. $30,000 per year in consulting income at age 57 is worth $30,000. That same nominal amount at 67 — if you have not raised your rates — is worth less in real terms. Whether the income keeps pace with inflation affects how much portfolio support you need in later years.

Whether it continues after full retirement. Some income sources — rental income, royalties, a small business — keep running after you stop actively working. Others stop when you stop showing up. The model needs to distinguish between the two.

How Semi-Retirement Changes Your FIRE Number

The standard FIRE calculation is simple: multiply your annual expenses by 25 to get the portfolio balance that can sustain a 4% annual withdrawal indefinitely. If you spend $80,000 per year, your number is $2,000,000. For FIRE planning with multiple income sources like this, see the guide on calculating your FIRE number with multiple income sources.

But if you plan to earn $40,000 per year part-time from ages 52 to 62, your portfolio only needs to cover $40,000 per year during that window — not $80,000. And after 62, the portfolio has been compounding on a much larger base because you were barely drawing from it.

The practical effect is that your required portfolio at the point you leave full-time work is substantially lower than the 25x number suggests. You do not need $2,000,000 to retire at 52 if you plan to earn $40,000 a year for the next decade. You might need $1,200,000 or $1,400,000, depending on your specific numbers.

This is why semi-retirement is so powerful as a FIRE strategy. It lets you leave the demanding career years earlier — before you have hit the full 25x number — while the portfolio continues growing during a lower-stress working phase. By the time you fully retire, you have often overshot the target anyway.

Common Semi-Retirement Scenarios and How They Model Out

The consulting phase. You leave a corporate job at 56 and pick up project-based consulting work at roughly half your old rate. You earn $50,000 to $70,000 per year for five to eight years, then wind it down entirely. This income should be modeled with an inflation adjustment — consulting rates tend to rise over time — and an end age where it stops completely.

The part-time job. You take a 20-hour-per-week job at something you enjoy — a local shop, a nonprofit, a golf course — for the health insurance or the structure as much as the income. You earn $25,000 to $35,000 per year. This often runs until Medicare eligibility at 65, at which point the health insurance motivation disappears. Model it with a flat or modestly inflation-adjusted income and an end age of 65.

The passion project that pays. You have a skill — writing, photography, coaching, woodworking — that generates some income but not a full salary. You earn $15,000 to $25,000 per year with no fixed end date. This may continue well into traditional retirement, especially if it is something you would do anyway. Model it with an inflation adjustment and set it to continue after your formal retirement date.

The rental income bridge. You own a rental property that generates $24,000 per year after expenses. This is not really work, but it is income that offsets portfolio withdrawals. It has its own dynamics — vacancy risk, maintenance costs, eventual sale — but for planning purposes it functions like part-time income with no fixed end date and modest inflation adjustment through rent increases.

What Happens at the Transition Point

The moment part-time income ends is the most important date in a semi-retirement plan. That is when the portfolio has to take over completely, and your balance at that point determines whether you are actually safe.

A common mistake is to calculate the FIRE number based on full retirement spending and then assume that having part-time income during the early years means you are fine. That logic only holds if you have actually modeled what the portfolio looks like when the income stops — not just at the point you left full-time work.

If you retire from your main career at 55 with $1,100,000 and plan to work part-time until 63, the question is not whether $1,100,000 is enough at 55. The question is what the portfolio looks like at 63 after eight years of partial withdrawals, and whether that balance is sufficient to support full retirement from 63 onward. Those are two very different questions.

Health Insurance Is the Variable People Forget

For anyone retiring before 65, health insurance is a significant expense that sits outside the standard retirement spending calculation. Individual market premiums for a 58-year-old can run $600 to $1,200 per month depending on plan and location — $7,200 to $14,400 per year.

One of the most common reasons people take part-time jobs in semi-retirement is specifically to get employer-sponsored health insurance, not for the income itself. If a part-time job at $30,000 per year comes with health coverage worth $12,000 in premiums, the effective value to your plan is $42,000 — the income plus the coverage you do not have to buy separately.

This is worth modeling explicitly. If part-time work provides health insurance through Medicare eligibility at 65, the income figure in your plan should reflect the full economic value: the earnings plus the avoided premium cost. That changes the math on how much portfolio you need before you can leave your main career.

How to Model This in a Calculator

What you need is the ability to enter income sources with a start age, an end age, an inflation toggle, and a flag for whether the income continues after your formal retirement date.

NumberToRetire.com handles this through the Additional Income section. You can add a part-time income source — label it "consulting" or "part-time job" — set the annual amount, the age it starts, whether it adjusts for inflation, and whether it continues after retirement. If your part-time income ends at a specific age, the projection correctly stops including it at that point and shows what the portfolio needs to cover from there forward.

You can add multiple sources independently. If you have rental income that continues indefinitely and consulting income that ends at 63, both are modeled correctly in the same projection. The chart shows the income streams separately from the portfolio balance, so you can see exactly when the portfolio takes over and what the balance looks like at that transition.

Run the projection twice — once with the part-time income included and once without — and compare the retirement dates. The gap between those two dates is the value of your semi-retirement plan in years.