Due Date Calculator Skill

Overview

Includes pregnancy milestones, percentage completion, and important dates like trimester transitions, perfect for pregnancy tracking and prenatal care applications.

The tool

Once your client is connected to the VerveKit server, this appears in its tool list as DueDateCalculatorSkill. It is read-only and open-world — it fetches and never mutates anything on your side — so most clients call it without asking you to confirm.

{
  "name": "DueDateCalculatorSkill",
  "arguments": {
    "last_period": "2025-06-01"
  }
}

You do not name the tool yourself; the model picks it. Asking about 2025-06-01 in the terms this skill covers is enough for it to reach for DueDateCalculatorSkill on its own — naming it explicitly also works, and is the way to force the call.

Connecting

One server URL covers every skill in the catalog, including this one. Authorization is OAuth: the client opens a browser once, and there is no key to paste into a config file.

{
  "mcpServers": {
    "vervekit": {
      "url": "https://api.vervekit.com/v1/mcp"
    }
  }
}

https://api.vervekit.com/v1/mcp

Per-client setup — Claude, Cursor, VS Code, ChatGPT — is on the MCP setup page.

Arguments

These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made. Premium arguments are accepted on every plan but only take effect on plans that include them.

What the model gets back

The result carries a structuredContent object matching the tool's declared outputSchema, so a client reads fields without parsing prose. status is "ok" and error is null on success; a null field means the value was not available for that input, not that the call failed.

{
  "status": "ok",
  "error": null,
  "data": {
    "calculation_method": "last_period",
    "last_period_date": "2024-01-01",
    "estimated_conception_date": "2024-01-15",
    "due_date": "2024-10-07",
    "current_progress": {
      "days_pregnant": 715,
      "weeks_pregnant": 102,
      "days_into_week": 1,
      "formatted": "102 weeks, 1 days",
      "trimester": 3,
      "percentage_complete": 255.36
    },
    "time_until_due": {
      "days": 0,
      "weeks": 0,
      "days_extra": 0,
      "formatted": "Past due date",
      "is_overdue": true
    },
    "upcoming_milestones": [],
    "important_dates": {
      "end_first_trimester": "2024-04-01",
      "end_second_trimester": "2024-07-08",
      "full_term_begins": "2024-09-16"
    },
    "disclaimer": "This is an estimate only. Due dates can vary. Consult your healthcare provider for medical advice."
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Failure modes

Errors come back as tool errors carrying a sentence the model can act on, not a bare status code. Error handling covers the full list.

A call costs 2 credits each time the tool actually runs; a model that reasons about the tool without calling it costs nothing.

Use cases

Pregnancy Tracking

Build pregnancy tracking applications with accurate due date calculations based on last menstrual period or conception date

Prenatal Care

Calculate gestational age for prenatal care appointments, monitoring fetal development, and scheduling medical tests

Maternity Planning

Create maternity planning tools with delivery date estimates, trimester breakdowns, and important date tracking

Milestone Tracking

Provide pregnancy milestone information with week-by-week pregnancy timeline and key development stages

Other ways to use Due Date Calculator Skill

Set up Due Date Calculator Skill on VerveKit, or reach the same source a different way. Your VerveKit account and credits work on all of them — one key, one balance.

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