# ISO date add months

`iso-date-add-months` · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Add a signed month count to a YYYY-MM-DD date, clamping the day to the target month.

**Use when you need to: iso date add months · add calendar months to an iso date · shift iso date by months.**

## Supported

- iso date add months
- add calendar months to an iso date
- shift iso date by months

## Not supported

- add days
- add seconds
- add years as a separate unit
- time zones
- locale month names
- fiscal calendars
- datetime with time
- ISO week arithmetic

## Behavior

- date is a proleptic Gregorian UTC calendar date YYYY-MM-DD with years 0001-9999.
- months is a canonical integer string with at most 6 digits excluding sign; -0 is accepted as 0.
- Month arithmetic uses index = year*12 + (month-1) + months, then year-prime = floor(index/12) and month-prime in 1..12.
- The day is clamped to the last valid day of the target month (31 January plus one month is 28 or 29 February).
- The result year must stay in 0001-9999.
- Output date is zero-padded YYYY-MM-DD.

## Input

- `date` (string, required): max length 10; pattern `^\d{4}-\d{2}-\d{2}$`
- `months` (string, required): max length 7; pattern `^-?(0|[1-9][0-9]*)$`

## Output

- `date` (string, required): max length 10; pattern `^\d{4}-\d{2}-\d{2}$`

## Limits

- min year: 1
- max year: 9999
- max months digits: 6

## Example

Request input:

```json
{
  "date": "2026-01-31",
  "months": "1"
}
```

Response:

```json
{
  "result": {
    "date": "2026-02-28"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "iso-date-add-months",
  "version": "1.0.0",
  "input": {
    "date": "2026-01-31",
    "months": "1"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/iso-date-add-months/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"date":"2026-01-31","months":"1"}'
```

The machine-readable contract is at [/v1/tools/iso-date-add-months/versions/1.0.0](/v1/tools/iso-date-add-months/versions/1.0.0).

### CLI

```sh
node cli.mjs run iso-date-add-months 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [ISO date add years](/tools/iso-date-add-years): Add a signed whole-year delta to a YYYY-MM-DD date, clamping the day if 29 February has no match.
- [ISO date-time add seconds](/tools/iso-datetime-add-seconds): Add a signed whole-second delta to a strict UTC ISO-8601 datetime.
- [ISO date add](/tools/iso-date-add): Add a signed whole-day delta to a strict YYYY-MM-DD calendar date.
- [ISO date age](/tools/iso-date-age): Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.
- [ISO date business day add](/tools/iso-date-business-day-add): Add a signed count of business days to a date, skipping caller-supplied weekend weekdays and holidays.
- [ISO date range split by month](/tools/iso-date-range-split-by-month): Split an inclusive [start, end] date range into per-calendar-month sub-ranges.