Nanny Share Math: The Cost Split, the Worked Example, and the Tax Trap

Last updated September 28, 2026

General information, not advice: this page covers tax and employment topics in general terms. It is not tax or legal advice, and reading it does not create a CPA–client relationship. Tax and labor rules vary by state and situation — consult a qualified professional for your circumstances.

A nanny share — two families splitting one nanny — looks like the perfect arbitrage: nanny-quality care at daycare prices. The cost math really is attractive. But the structure most families use contains a tax trap that nobody mentions at the playground: each family is a separate household employer, with its own EIN, its own Schedule H, and its own FICA obligation on its share. Get the split right and the share is the best deal in childcare. Get the employer part wrong and both families have a compliance problem.

How cost splits work

There’s no single standard, but three models cover nearly every share:

Model 1: The 2/3-each norm (most common). Each family pays roughly two-thirds of what they’d pay a nanny solo. The nanny earns about 4/3 of a single-family rate — a premium for the extra work of two families’ kids, two sets of parents, and two households’ logistics. This is the market-clearing arrangement: the nanny earns more than solo, each family pays less than solo.

Model 2: Straight 50/50. Simpler, common when both families have one child of similar age and identical schedules. The nanny earns the same as a solo placement while doing more work — which is why experienced share nannies often prefer the 2/3 model.

Model 3: Weighted by usage. Families with different schedules or different numbers of children split proportionally — e.g., one family uses 30 hours/week and the other uses 20, so the split is 60/40. Fairest on paper; requires the most bookkeeping and the most renegotiation when schedules drift.

Whatever the model: put the split formula in writing, including what happens when one family’s schedule changes. “We’ll figure it out” is how shares die.

The worked example: $25/hour

Assume a nanny whose solo rate would be $25/hour, working 40 hours/week for two families with one child each, using the 2/3-each model:

Nanny’s hourly rate in the share: $25 × 4/3 ≈ $33.33/hour
Each family’s hourly cost: $33.33 ÷ 2 ≈ $16.67/hour
Each family’s weekly gross wages: $16.67 × 40 = $666.67/week
Each family’s annual gross wages: $666.67 × 52 = $34,667/year
Each family’s employer FICA (7.65%): $2,652/year
FUTA per family: 0.6% on the first $7,000 of each family’s wages = $42
Each family’s all-in annual cost: roughly $37,400–$37,800 (plus state unemployment and workers’ comp, which vary by state)

Compare: solo nanny at $25/hr all-in ≈ $57,000/year. Each share family saves roughly $19,000–$20,000/year — a 34% discount — while the nanny earns $69,333 instead of $52,000, a 33% premium. That mutual gain is why shares work. The nanny’s premium compensates for genuinely harder work: two infants are more than twice the work of one.

The part-time wrinkle: if the share is 25 hours/week instead of 40, each family’s annual wages are ~$21,667 — still well above the $3,000/year FICA threshold, so the employer tax obligations apply in full. Shares don’t get small enough to dodge household-employer status.

THE TRAP: two families, two employers

This is the section that justifies this page’s existence. In a nanny share:

Each family is a separate household employer. There is no “the share” as a tax entity. Family A and Family B each obtain their own EIN, each file their own Schedule H with their own Form 1040, each issue their own W-2 to the nanny (reporting only their share of wages), and each owe FICA on their share.
You cannot have one family “run payroll” for both. If Family A pays the nanny the full $69,333 and Family B reimburses half, Family A has overstated its wages (and owes FICA on all of it) while Family B has an undocumented arrangement with no W-2 to support its share. The correct structure is two parallel payrolls — which in practice means one payroll service running two household accounts, or each family using its own service.
State registrations double too. Each family registers for state unemployment insurance separately and carries its own workers’ comp policy (where required).

The clean setup: agree on the gross hourly rate and the split in a written share agreement between the families (separate from each family’s work agreement with the nanny), then each family runs its own payroll on its share. A payroll service can usually handle both accounts; confirm before signing up.

Overtime complications in shares

Overtime is where share math gets genuinely tricky. Federal law requires 1.5× beyond 40 hours/week for non-live-in domestic workers — but 40 hours per employer or combined? Under the FLSA’s joint-employment rules, hours worked for two families can be aggregated when the families are effectively joint employers of the same worker — which, in a share where both families direct the nanny’s work during shared hours, is a live question. If aggregation applies and the nanny works 40 shared hours plus 5 extra hours for one family, those 5 hours may be overtime — and which family owes the premium is its own dispute.

Practical handling: cap the share at 40 total hours in the written agreement, define an overtime rate and which family pays it before it happens, and get professional advice on the joint-employment question in your state. This is the one share issue worth paying a payroll service or employment attorney to get right, because the liability runs to both families.

Why shares fall apart (and how to prevent it)

In rough order of frequency:

Schedule drift. One family’s hours creep; the other family subsidizes coverage it doesn’t use. Prevention: the written split formula includes a renegotiation trigger (e.g., “if either family’s scheduled hours change by more than 5/week, the split reprices”).
Unequal sick days and vacations. Family A’s nanny-share weeks get consumed by Family B’s vacations — under guaranteed hours, the nanny is paid either way, but the value each family receives diverges. Prevention: align vacation calendars annually; the share agreement states each family gets the same paid-time-off value.
Parenting-style friction. Different discipline, screen-time, and feeding rules in one caregiver’s day. Prevention: discuss before starting, write the shared rules down, and accept that the stricter family’s rules usually govern shared time.
One family exits. A move, a job change, a second child — shares end. Prevention: the share agreement includes an exit clause: notice period (60–90 days is fair), what happens to the rate for the remaining family (it typically rises toward the solo rate), and whether the exiting family helps find a replacement.
The nanny burns out. Two families’ logistics, two sets of expectations, no downtime between “employers.” Prevention: pay the 2/3 premium rather than 50/50, protect her breaks, and remember she’s doing the hardest version of the job.

Separate from the nanny’s work agreement, the two families should sign:

The cost-split formula and the repricing trigger
The schedule, including whose home hosts and how hosting rotates (or doesn’t)
Vacation/sick-day alignment and guaranteed-hours treatment
Overtime rate, cap, and who pays
Supplies and expense splitting (diapers, food, activities)
The exit clause: notice period, rate adjustment, replacement duty
Confirmation that each family will run its own payroll and file its own Schedule H

A nanny share is the best value in childcare when it’s structured like the two-employer arrangement it legally is — and a mess when it’s structured like the casual handshake it socially feels like.