Two-phase retirement math
FIRE calculator with Social Security
Estimate how Social Security may reduce the later portfolio-funded spending gap without incorrectly using future benefits to fund the early-retirement bridge.
Social Security can reduce the amount a portfolio must provide after benefits begin. It does not fund the years before claiming, and a simple subtraction can understate the bridge required for early retirement.
Use the calculator below for the later steady-state gap, then separately reserve for the pre-benefit years.
Interactive estimate
Later-income gap calculator
Estimate the portfolio target after gross Social Security or pension income begins. Fund the years before those payments separately.
Gross annual Social Security
$30,000
Later annual portfolio gap
$42,000
Target after income begins
$1,050,000
Educational estimates only, not individualized Social Security, tax, investment, or financial advice. Claim estimates are retired-worker comparisons based on the FRA amount you enter; verify benefits with SSA. Federal taxable-benefit estimates exclude state tax and special IRS worksheet situations. They use the gross benefit entered above and do not apply ordinary repayments or Form SSA-1099/RRB-1099 net box 5. Exact inputs and results stay in this browser.
Two-phase method
- Phase 1: retirement date through the year before benefits begin. The portfolio covers the full spending gap.
- Phase 2: benefit years. Subtract expected Social Security and other durable income from spending.
- Stress both phases for taxes, benefit uncertainty, survivor changes, and poor early returns.
Example
A household spends $72,000 and expects $30,000 of annual Social Security beginning in ten years. At 4%, the later steady-state gap of $42,000 corresponds to $1.05 million. That does not include the first ten years of larger withdrawals, so $1.05 million is not the complete retirement target.
What this quick calculator omits
- Benefit taxation and account-specific withdrawal taxes.
- Cost-of-living adjustments and claiming-age tradeoffs.
- Survivor and spousal benefit rules.
- Sequence risk during the bridge.
Frequently asked questions
- Does a FIRE number include Social Security?
- A basic FIRE number usually does not. Social Security can be modeled as later income that reduces the spending gap after benefits begin.
- Can I subtract my full estimated benefit?
- Use a conservative, current estimate and account for taxes, claiming age, and timing. Do not subtract it from years before it begins.
- What if I plan to claim at 70?
- The later benefit may be higher, but the portfolio must fund a longer bridge. Compare both the benefit amount and the additional bridge withdrawals.
Keep planning
Educational illustration only — not financial, investment, tax, legal, medical, or insurance advice. Calculations use simplified assumptions and do not predict future returns or benefits.