Daycare charges per child; a nanny, a nanny share, and an au pair charge by the arrangement — flat whether you have one kid or three. That single pricing difference is what flips the cheapest option as your family grows. Enter your hours and rates to price all four apples-to-apples.
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Which care option costs your family least?
Daycare, nanny, nanny share, au pair — weekly, per-child, and yearly — for your kid count.
How it works: daycare is priced per child — weekly rate × kids. A nanny and a nanny share are priced flat by the hour — hourly rate × weekly hours, no matter how many kids. An au pair is priced flat too: weekly stipend + yearly agency fee ÷ 52 + the room & board value. The winner is the lowest weekly cost at your kid count. One honesty note: this compares headline rates — a legally paid nanny also carries household-employer payroll taxes (roughly 10–11% on top of wages), and daycare quotes often exclude registration or activity fees. Use this to rank the options, then confirm with real quotes.
How childcare cost math works
Two pricing models fight over your childcare bill. Daycare charges per child: every extra kid adds the full weekly rate. Nannies, nanny shares, and au pairs charge for the arrangement: the price is set by hours, stipends, and fees — flat whether you have one kid or three. So the cheapest option at one kid is very often not the cheapest at two or three, and the curves above show exactly where the flip happens.
The au pair wins by $77.31 a week — about $4,020 a year. Now try "1 child" in the scenarios above: daycare drops to $330 and takes the lead, because per-child pricing only hurts you when there is more than one child to multiply.
Where this comes in handy
Growing families: the flip point — run 1, 2, and 3 kids and watch the flat options take over as the family grows.
Au pair math: the agency fee is the forgotten line item — spreading it over 52 weeks is what makes the true weekly price honest.
Nanny share: discounted rate, flat across kids — the middle ground when a full nanny is too rich but daycare does not fit.
Real quotes: plug in your local rates — the defaults are national starting points, not your city's prices.
Tax breaks: whichever option you pick, some of it may come back through the dependent care FSA or the childcare tax credit — run that comparison too.
For the full walkthrough — collecting quotes, converting every option to one weekly number, the per-child test, and the hidden extras — see the guide How to compare childcare costs.
Why does the cheapest option change when I add a kid?
Because two different pricing models are competing. Daycare multiplies: each kid adds the full weekly rate, so it climbs in steps. Nannies, shares, and au pairs are flat: the price is set by hours or program fees, so it does not move when a sibling arrives. The per-child test says it all — divide each flat total by your kid count and watch it fall below daycare once you hit two or three.
What am I missing in the au pair total?
The usual blind spot is everything beyond the stipend. The honest weekly price is stipend + agency program fee ÷ 52 + room & board value — the fee alone is roughly $9,000–$11,000 a year depending on the agency, which is over $180 a week people forget to count. Some families also add a phone plan, car insurance, or a higher education allowance; if you would, add them to the stipend line. Host families must provide a private bedroom, so the room value is a real cost of the arrangement.
Is a nanny share really that much cheaper than a nanny?
Typically yes — the share rate usually runs 25–35% under a full nanny’s hourly rate, because one caregiver’s day is split across two families. And because it prices flat by the hour like a full nanny, the multi-kid math favors it the same way. The trade-off is flexibility: you coordinate schedules, sick policies, and holidays with the other family, and some caregivers cap the total number of children.
Do I have to add employer taxes for a nanny?
If the nanny is paid legally, yes — household-employer payroll taxes run roughly 10–11% on top of wages (Social Security, Medicare, unemployment). This calculator shows headline rates so you can compare the structure of the options; add the tax slice to whichever hourly option wins before you decide. A nanny agency may also charge a placement fee worth a few thousand dollars.
What about sick days, vacations, and holidays?
They tilt the comparison. Daycare charges whether your child attends or not — you pay through their spring break. Nannies (and shares) normally get paid time off and paid holidays written into the contract, so you pay for care you don’t use. Au pairs also get paid time off under program rules. None of this shows in the weekly math, but over a year it is worth a few hundred dollars of difference.
Are the default rates accurate for my city?
They are national starting points, not local quotes — coastal metros routinely run higher, smaller markets lower. Treat the defaults as the shape of the comparison and edit them with two or three local quotes. The structural insight travels: whatever your local numbers, per-child pricing still climbs and flat pricing still holds still.