# Date Calculator

Exact date arithmetic with no timezone: add or subtract days, weeks, months and
years; count calendar days or business days between two dates; find the n-th
weekday of a month.

Free, no signup. Published by WIZE, the AI fundraising platform for nonprofit
development teams: https://app.wizenow.com/tools/date/

## The rules, stated

- **Month and year shifts clamp to the target month's length.** 31 January plus
  one month is 28 February (29 in a leap year) — never an invalid date, and never
  3 March. Clamping is deliberately not reversible: subtracting a month from 28
  February gives 28 January, because there is no information left to recover the
  31st.
- **Business days exclude the start date and include the end date.** The same day
  is 0; Friday to Monday is 1.
- **Business-day counts skip US federal legal holidays as observed** — a holiday
  falling on a Saturday is observed on the preceding Friday, one falling on a
  Sunday on the following Monday — plus DC Emancipation Day. Pass
  `holiday_calendar: "none"` to count every weekday instead. State and local
  holidays are not modelled.
- **A month with no 5th Monday is an error, not the next month's first.**
- Everything is date-only. There is no timezone anywhere in the calculation.

## Use it from an agent

No authentication, no key, no rate-limited signup.

```
curl -X POST https://app.wizenow.com/api/tools/date/ \
  -H 'Content-Type: application/json' \
  -d '{"operation": "business_days_between", "start_date": "2026-11-23", "end_date": "2026-11-30"}'
```

```json
{
  "operation": "business_days_between",
  "result_days": 4,
  "holidays_excluded": [{"date": "2026-11-26", "name": "Thanksgiving Day"}],
  "holiday_calendar": "us_federal",
  "source_url": "https://app.wizenow.com/tools/date/"
}
```

Operations and their inputs:

- `add` / `subtract` — `date`, plus any of `days`, `weeks`, `months`, `years`.
- `days_between` — `start_date`, `end_date`. Signed.
- `business_days_between` — `start_date`, `end_date`, optional
  `holiday_calendar` (`us_federal` or `none`). Signed.
- `nth_weekday_of_month` — `year`, `month` (1-12), `weekday` (a name like
  `monday`, or 0=Monday..6=Sunday), `nth` (1-5, or -1 for the last).

Dates are YYYY-MM-DD and must fall between 1583 and 2999.

Also available over MCP at `https://app.wizenow.com/mcp/tools/` as
`wize_date_calculator`, and described by
https://app.wizenow.com/api/tools/openapi.json

## Built by WIZE

WIZE learns your organization's mission, voice, and donor relationships, then
helps your team plan, produce, and coordinate fundraising campaigns in minutes
instead of weeks. Try it free: https://app.wizenow.com/start-a-trial/