Factor your pension into your financial independence plan. See how a defined benefit or defined contribution pension changes your FIRE number and timeline.
What Is a Pension-Adjusted FIRE Number?
The standard FIRE number calculation is simple: take your annual expenses in retirement and divide by your safe withdrawal rate (usually 4%). If you spend $60,000 a year, your FIRE number is $1.5 million.
The problem is that formula assumes your portfolio has to cover 100% of your expenses forever. If you have a pension coming, that is not true. A defined benefit pension of $2,000 a month is $24,000 a year of guaranteed income. That shrinks your portfolio requirement significantly.
But it is rarely as simple as just subtracting pension income from expenses. The tricky part is timing. If you want to retire at 50 and your state pension does not start until 67, you have a 17-year bridge period where your portfolio needs to cover everything on its own. This calculator handles that math.
Defined Benefit vs. Defined Contribution: What Is the Difference?
These are the two main types of pension, and they require completely different approaches in your FIRE planning.
A defined benefit (DB) pension pays a guaranteed monthly income from a specified age. Final salary schemes, state pensions, military pensions, and many public sector pensions fall into this category. You know (roughly) what you will receive and when. The uncertainty is whether you will FIRE before that date.
A defined contribution (DC) pension is a pot of money you build up through contributions and investment growth. 401(k), SIPP, workplace pension: these are all DC. You own the pot, but you cannot touch it until the access age (57 in the UK, 59.5 in the US). If you FIRE at 45, you are waiting 12 years before that money is available.
The planning challenge for DC pensions is sizing your accessible portfolio to bridge the gap. The calculator does this automatically: it projects your pension pot to the access age, determines how much your accessible portfolio needs to be at FIRE, and gives you a combined target.
How the Bridge Period Works
This is the part most early retirement calculators skip. If you retire at 50 and your pension starts at 65, you have a 15-year bridge period. During those 15 years, your portfolio must cover 100% of your expenses with no pension income.
The bridge portfolio calculation works backwards from the pension start date:
- First, calculate how much portfolio you need when the pension kicks in (to sustain reduced expenses after pension income)
- Then, calculate the present value of that target at your FIRE date, plus the cost of funding expenses during the bridge
- That combined figure is your actual FIRE number
It sounds complicated because it is. But the result is almost always less than the no-pension FIRE number, sometimes dramatically so. A $2,000/month pension starting at 65 can reduce a $1.5M FIRE target down to $900,000 or less, depending on when you FIRE and your return assumptions.
What Return Rate Should I Use?
The calculator defaults to 7%, which is the approximate real (inflation-adjusted) long-run return of a diversified equity portfolio based on historical data. If you are more conservative or closer to retirement, 5-6% is reasonable. The difference compounds significantly over a long FIRE timeline, so it is worth running the numbers at different rates.
Do not use nominal returns without adjusting for inflation. If your investments return 10% but inflation is 3%, your real purchasing power grows at roughly 7%. Planning with nominal returns overstates how much your money will actually buy in retirement.
How Accurate Is My Projected Pension Amount?
For defined benefit pensions, the amount depends on years of service and salary. If you leave a job early (which you would, if you FIRE), your pension is usually based on your accrued service to that point rather than projected full service. Most DB pension schemes let you request a current entitlement statement.
For defined contribution pensions, the pot size at access depends on contributions and returns over the coming years. The calculator projects this using compound growth, which is a reasonable estimate but not a guarantee. Markets vary. Contributions change. Run the calculation periodically as your situation updates.
Frequently Asked Questions
What if my pension starts before my target FIRE age?
If your pension starts at or before your FIRE age, the bridge period is zero. Your FIRE number is simply the reduced expense amount (annual expenses minus pension income) divided by your safe withdrawal rate. This is the ideal scenario and results in the lowest possible FIRE number.
Should I count employer pension contributions in my DC pot contributions?
Yes. If your employer matches 5% and you contribute 5%, your total contribution rate is 10% of salary. Enter the combined number. Employer matches are free money and can significantly accelerate your pension pot growth.
Can I access my DC pension early in an emergency?
Generally no, not without significant tax penalties. In the US, early 401(k) withdrawals before 59.5 face a 10% penalty plus income tax. In the UK, accessing a SIPP before 57 (rising to 57 in 2028) is typically not permitted except in cases of serious ill health. This is why sizing your bridge portfolio correctly matters: you cannot count on early pension access as a safety net.
Does this account for inflation?
The calculator assumes your return rate is a real (inflation-adjusted) rate. If you enter 7%, that should represent returns above inflation. Your pension amount and expenses should be in today’s dollars. Some DB pensions are index-linked (they increase with inflation), which makes them more valuable. DC pots grow with investment returns, which historically outpace inflation over the long term.
What about Social Security or State Pension in addition to a workplace pension?
If you have both, you can treat the total guaranteed income as your DB pension amount in this calculator. Add your expected Social Security or State Pension amount to your workplace pension income and enter the combined monthly figure. This will give you the most accurate reduced FIRE number.
The Short Version
A pension changes your FIRE number, sometimes dramatically. The key variables are the pension amount, when it starts, and the gap between your FIRE age and pension start age. If you are retiring early with a pension that starts later, you need a bridge portfolio to cover the gap. This calculator handles all of that automatically. Use it alongside the standard FIRE calculator to see the full picture.