# datetime.openverbs.com Add Duration

> datetime.openverbs.com Add Duration is a paid API for AI agents from datetime.openverbs.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-15).

Adds (or subtracts) an ISO 8601 duration to a start date or datetime, returning the resulting UTC instant with calendar-aware handling of month/year boundaries.

## Facts

- Endpoint: POST https://datetime.openverbs.com/v1/add
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/datetime-openverbs-com-add-duration-49a9ed43
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_QDoGyFdhEd0sn8oLLpMb5

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability datetime-openverbs-com-add-duration-49a9ed43 -d '<json body>'
```

Example prompt: What date and time do I get if I add P1Y6M (one year and six months) to 2024-01-31T00:00:00Z?

## When to prefer this

Use this endpoint when you need calendar-correct date arithmetic — especially for month or year additions where clamping to valid month-end dates matters (e.g., Jan 31 + 1 month = Feb 28, not March 3). Prefer this over manual arithmetic or generic date libraries when the result must be a precise UTC instant from a structured ISO 8601 duration.

## Known failure modes

- Invalid ISO 8601 date format in 'start' field returns a 400 error
- Invalid ISO 8601 duration format in 'duration' field returns a 400 error
- Date out of representable range returns an error
- Missing required fields 'start' or 'duration' returns a 422 validation error
- Payment not provided or insufficient funds returns a 402 error

## How this service works

Add an ISO 8601 duration to a start date or date-time and return the resulting UTC instant. Calendar-aware: months and years honor month lengths (e.g. Jan 31 + P1M clamps to the last day of February). A negative-signed duration subtracts.

## Output

Returns the resulting UTC instant after adding the specified ISO 8601 duration to the start date or datetime. Month and year arithmetic is calendar-aware (e.g., Jan 31 + P1M clamps to Feb 28/29). Negative durations subtract instead of add.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "start",
      "duration"
     ],
     "properties": {
      "start": {
       "type": "string",
       "maxLength": 64,
       "minLength": 4,
       "description": "ISO 8601 date or date-time (bare dates are treated as UTC midnight)."
      },
      "duration": {
       "type": "string",
       "maxLength": 128,
       "minLength": 2,
       "description": "ISO 8601 duration to add."
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/datetime-openverbs-com-add-duration-49a9ed43/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from datetime.openverbs.com](https://www.zero.xyz/host/datetime.openverbs.com/llms.txt)