PlainlyKit Date API

Add weeks to a date and get the resulting date, weekday, and number of days as JSON. This API uses the same calendar calculations as our weeks from today calculator.

Free to use. No account or API key required. Download the OpenAPI 3.1 specification.

Make a request

curl 'https://plainlykit.com/api/v1/weeks-from-date?start=2026-10-18&weeks=6'

Open the example response

Parameters

Send a GET request to /api/v1/weeks-from-date with both query parameters:

• start: a valid date in YYYY-MM-DD format, from year 0001 through 9999.
• weeks: a whole number from 0 to 5200, without leading zeros. One week is exactly seven days.

Dates use the Gregorian calendar and UTC date-only arithmetic. Local time zones and daylight saving changes do not change the answer. The result must stay within year 9999. Repeated or unknown parameters are rejected.

Response

{
  "start": "2026-10-18",
  "weeks": 6,
  "days": 42,
  "date": "2026-11-29",
  "weekday": "Sunday"
}

Successful requests return 200. Invalid requests return 400 with an error message. For example, 2026-02-29 is rejected rather than silently moved to March.

Using the API

Cross-origin requests are supported, so you can call this endpoint from a browser or a server. Responses for the same inputs are cacheable for one day. Cache results and avoid unnecessary repeated requests. Availability is provided on a best-effort basis, without an uptime guarantee.

This endpoint accepts dates and week counts. It has no file upload, account, or database. Our privacy page explains hosting and analytics. For questions or errors, contact [email protected].

Prefer an interactive tool? Try weeks from today or see 6 weeks from today.