Schedule and cost ledger for nanny shares

The idea

A nanny share moves USD 4-6k a month between three parties, governed by a text thread and Venmo memos. The maths is genuinely fiddly: shared hours split one way, the Tuesday one family was on holiday splits another, the nanny’s guaranteed 40 hours must be topped up when a light week undershoots, and PTO accrues regardless. Every share has one parent doing this in a spreadsheet, and every disagreement about it is a disagreement between families who see each other daily.

The wedge is encoding the share-specific rules nothing else models: uneven splits for solo days, guaranteed-hours top-ups, overtime, PTO accrual. The monthly statement shows its working line by line and locks only when both families approve it, converting a monthly negotiation into a monthly click.

Who pays

The share itself: GBP 12 a month against a GBP 3-4k monthly spend, split two ways, bought by whichever parent currently owns the spreadsheet and resents it. Nanny shares cluster intensely in specific city neighbourhoods, so distribution is local parent listservs and Facebook groups where shares are formed, plus nanny agencies and share-matching sites that get asked “how do we handle the money” by every new pairing. SEO on “nanny share cost calculator” catches formation-stage intent.

MVP scope

• Rate rules setup: shared/solo rates, guaranteed hours, overtime, PTO accrual
• Weekly schedule grid with per-family attribution and absence block types
• Auto-generated monthly statement per family with visible calculations
• Dual approval that locks statements; adjustment lines for corrections
• Nanny read-only access, Stripe subscription billing
• Skip for v1: actual payment processing or payroll, tax documents, nanny timesheet clock-in, and shares of three or more families

Build ShareLedger, a web app that manages the schedule and money maths of a two-family nanny share. Stack: Next.js (App Router), Supabase (Postgres + magic-link auth), Stripe.

Core flow: one parent creates the share, invites the other family and optionally the nanny (read-only). Setup captures the rate rules: hourly rate for shared care, hourly rate for solo care (one family's kids only), guaranteed weekly hours minimum, overtime threshold and multiplier, and the nanny's PTO accrual rate. Each week has a schedule grid where blocks are attributed to Family A, Family B, or Both; sick days, holidays, and nanny PTO are logged as block types.

At month end the app generates a statement per family: shared hours split by the agreed ratio, solo hours attributed fully, guaranteed-hours top-up if scheduled hours fell short, overtime, and PTO accrued/used. Both families tap Approve; the statement locks and archives.

Pages: setup wizard (rate rules), weekly schedule grid, monthly statement view with line-item breakdown, statement archive, and share settings.

Implementation details: the guaranteed-minimum rule is where every spreadsheet breaks — if total paid hours fall below the guarantee, the top-up must be split by each family's share of scheduled (not actual) hours that month; encode this explicitly and show the working on the statement. Statements are immutable once dual-approved; corrections go on the next statement as labelled adjustment lines.

Pricing: GBP 12/month per share via Stripe, first month free, split naturally by the two families.