Couples Mixed-Finance Planner — Methodology

How This Calculator Works

Most retirement tools treat a couple as one person with one pot of money. This planner does not. It models two people with their own earnings records, their own accounts, and their own claiming decisions, then shows the combined outcome.

It covers four things: how contributions split between joint and separate accounts, the Social Security claiming age for each partner including spousal benefits, the combined FIRE number against each partner's individual number, and an optional pension.

Inputs and Assumptions

• Each partner's age, income and savings: Held separately throughout — the two are never merged into one earner.
• Joint and separate allocation: How income flows into shared versus individual accounts.
• Claiming ages: Chosen for each partner from their current age (62 at the earliest) to 70, so all 81 pairs only when both are 62 or younger, maximising benefits collected to age 85, since staggered claiming is often better than both claiming together. A partner already 70 or older is treated as claiming at 70, when delayed credits stop (20 CFR 404.313(b)). A spousal top-up starts only once the other partner has filed.
• Pension: Optional, applied to the partner who holds it.

Full Retirement Age is estimated from each partner's current age.

Formula

// Primary Insurance Amount per partner — 2026 bend points
tier1 = min(AIME, 1286) × 0.90
tier2 = max(0, min(AIME, 7749) − 1286) × 0.32
tier3 = max(0, AIME − 7749) × 0.15
PIA   = tier1 + tier2 + tier3

// Own benefit: reduced 5/9% a month for the first 36 months
// before FRA and 5/12% beyond; +2/3% a month after FRA to 70.

// Spousal top-up (when own PIA < half the other's PIA):
excess  = 0.5 × otherPIA − ownPIA
top-up  = excess reduced 25/36% a month (first 36) and 5/12%
          beyond, at the age it starts; no delayed credits
starts  = when the other partner has filed, not before
          your own claim (applying for one is applying for both)
total   = max(own, own without delayed credits + top-up)
// i.e. 50% of the higher earner's PIA at FRA — NOT 50% of
// a delayed age-70 benefit, and not raised by your own credits.

lifetime to 85 = own × years from claim + top-up × years from start

combinedFireNumber = combinedAnnualSpending × 25

Data Sources

• Social Security Administration — Primary Insurance Amount formula and the 2026 bend points ($1,286 and $7,749).
• SSA spousal benefit rules — one-half the worker's PIA (20 CFR 404.333), entitlement only once the worker is entitled (20 CFR 404.330), reductions for age (20 CFR 404.410), no delayed credits for spouses (20 CFR 404.313(e)).
• Own benefit plus spousal excess — 42 U.S.C. 402(q)(3)(B) and 402(k)(3)(A); SSA POMS RS 00615.020 and RS 00615.694.
• Deemed filing — Bipartisan Budget Act of 2015, section 831; SSA POMS GN 00204.035.
• For official, personalised projections use ssa.gov/myaccount.

Limitations

• Historical earnings are not wage-indexed. The SSA indexes past earnings to national wage growth before averaging; this planner does not. Treat Social Security figures as approximations.
• Full Retirement Age is estimated from current age rather than an exact birth date.
• Uses 2026 bend points, which are adjusted annually.
• Assumes neither partner has started Social Security. A claim already made is fixed, and the planner has no input for it, so its recommendation does not apply to a partner who has claimed.
• Does not model survivor benefits, which are often the decisive factor in a couple's claiming strategy.
• Does not model divorced-spouse benefits — see the Social Security Divorced calculator for those.
• Does not model the tax treatment of Social Security benefits, which depends on combined income.
• Does not model state-specific rules, community property, or prenuptial arrangements.
• The 25× FIRE multiple assumes a 4% withdrawal rate, which is a rule of thumb, not a guarantee.

Last Updated

July 2026 — Methodology page published (engine then used the 2024 SSA bend points).

October 2026 — Engine moved to the 2026 SSA bend points ($1,286 and $7,749), from the shared source src/lib/tax/data/social-security.ts.

October 2026 — Spousal benefits no longer earn delayed retirement credits and are reduced on the spousal schedule, as an own benefit plus a top-up that starts once the other partner has filed. Previously a lower earner claiming at 70 was shown 124% of the spousal amount (for example $1,736 instead of $1,400).

October 2026 — Claiming ages are searched from each partner's current age. Previously the search always started at 62, so a 68-year-old could be told to claim at 67.