A household rarely retires as one unit, so the projection doesn't force it to. Each earner is modeled as their own stream, on their own clock.
- Contributions are per-earner. Each stream (salary, savings rate, employer match) belongs to one owner and routes into that owner's account group. A spouse's 401(k) deferrals therefore build the spouse's tax-deferred balance, not a household blob.
- Retirement is per-earner. The spouse retires at their own age; internally the engine converts it onto the primary's age clock, but you enter it as the spouse's age. Staggered retirements fall out naturally, with one income continuing while the other stops, including the bridge years where the household lives partly on the working spouse's salary.
- Payroll tax is real. Working-years wages carry household FICA, so pre-retirement cash flow isn't overstated.
- Ages drive entitlements separately. Social Security claim ages are per person, and RMDs key off each owner's own birth year via the account's owner.
This is why accounts have owners in the Profile: the engine needs to know whose tax-deferred dollars they are to get RMD timing, conversion room, and the survivor scenario right.