Every week, someone asks their AI assistant: "How much would I owe in taxes if I pay my nanny $35,000 a year?" The AI guesses. Sometimes it's close. Sometimes it's wrong — especially on state-specific rates that change annually across 50 states.
We kept seeing this. We also kept getting emails from CPAs and developers asking if we had an API. We didn't. So we built one.
What does the nanny tax API return?
You send a state and wage amount. You get back a complete tax breakdown — every line item, per-paycheck cost, and threshold status. Every number comes from current-year tax data we maintain.
curl -X POST https://www.nannykeeper.com/api/v1/calculate \
-H "Authorization: Bearer nk_live_YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"state":"CA","annual_wages":35000,"pay_frequency":"biweekly"}'
The response includes employer taxes, employee tax estimates, and a plain-English explanation of what it all means. The free tier gives you 50 requests per day — email only, no credit card.
Why does an MCP server matter for nanny taxes?
MCP lets AI agents call external tools during conversation. With our MCP server installed, when you ask Claude about nanny taxes, it calls our API instead of pulling from training data.
{
"mcpServers": {
"nannykeeper": {
"command": "npx",
"args": ["@nannykeeper/mcp-server"],
"env": { "NANNYKEEPER_API_KEY": "nk_live_YOUR_KEY" }
}
}
}
The difference: "you'd owe roughly 8-10%" becomes "you'd owe $2,957.50 in employer taxes in California — $2,170 Social Security, $507.50 Medicare, $42 FUTA, $238 state unemployment." Specific numbers from real data.
Who would use a nanny tax API?
Families with AI tools. Your AI assistant gets real tax data instead of approximations.
CPAs and tax preparers. The Professional tier handles up to 50 employer accounts from one API key. No clicking through a UI for each client.
Developers. Household employment tax rules span 50 different state configs, family member exemptions, and quarterly thresholds that vary by state. The API handles the complexity so you don't have to.
How much does the API cost?
The calculator is free forever. Running payroll, generating W-2s, and processing direct deposit require a paid plan — same prices as the web app.
| Plan | Price | Rate limit |
|---|---|---|
| Free | $0 | 50/day |
| Starter | $10/mo | 500/day |
| Plus | $18/mo | 2,000/day |
| Professional | $20 + $6/employer | 2,000/day |
What we learned building it
The hardest part was deciding what belongs in the free tier. Give away too much and nobody upgrades. Too little and nobody uses it.
We landed on this: the free tier answers "how much would I owe?" Only paid plans answer "ok, do it for me." The calculation is the hook. The payroll is the product.
The second challenge was making responses useful for AI agents. A JSON blob of tax numbers works for developers, but an AI needs context — what does this number mean, what should the user do next, is this above the threshold. We added limitations, next_actions, and threshold explanations so the AI can relay information naturally.
Ready to simplify nanny taxes?
NannyKeeper handles the calculations, deadlines, and paperwork so you can focus on your family.
FAQ
Can I use the API for free? Yes. The free tier gives you 50 calculations per day — all 50 states, full tax breakdown. No credit card, no time limit.
What's the difference between the API and the web calculator? The web calculator is a simplified estimate. The API returns a more detailed breakdown including employee-side estimates, threshold status, and per-paycheck cost — in a structured format you can parse programmatically.
Do I need an account to get an API key? You need an email address. That's it. Get one at nannykeeper.com/developers/keys.