# Duty stacking (POST /v1/calculate/stacking)

> POST /v1/calculate/stacking: Duty stacking. border.bot API reference (Landed cost).

Source: https://border.bot/docs/api/duty-stacking

> Documentation index: https://border.bot/llms.txt. Every page is Markdown at its URL + `.md`.

`POST https://api.border.bot/v1/calculate/stacking`

Requires an API key (`Authorization: Bearer bb_live_…`).

Which duty lines apply to a code from an origin on a date, without a shipment: the base duty, then every additional measure (Section 301, 232, reciprocal…), which exemption codes remove which, the measures that depend on metal content or a claim, and the claim codes you could file. Up to 100 lines; free unless your pricing says otherwise. Answers from border.bot’s own data: a destination it doesn’t cover returns 422 `unsupported_country`.

API key scope: `calculate`.

## Headers

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `idempotency-key` | string | no | Make retries safe: a repeat with the same key returns the original result without charging again (keys are scoped to your workspace). |

## Request body (JSON)

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `items` | object[] | yes |  |

## Responses

- `200`: Each line’s stack. (`StackingResponse`)
- `400`: Invalid input (`invalid_input`). (`Error`)
- `401`: Missing, invalid, revoked or expired API key (`unauthorized`). (`Error`)
- `402`: Not enough credits (`insufficient_credits`). Nothing was charged. (`Error`)
- `403`: Workspace suspended, action disabled, or the key lacks the scope (`org_suspended`, `action_disabled`, `forbidden`). (`Error`)
- `409`: A request with this Idempotency-Key is still in progress (`conflict`). (`Error`)
- `422`: A destination border.bot’s own data doesn’t cover yet (`unsupported_country`). (`Error`)
- `429`: Rate limited (`rate_limited`). Retry after `Retry-After` seconds; `RateLimit` says which limit was hit (`r=0`, `t` seconds until its window ends) and `RateLimit-Policy` its quota. (`Error`)
- `500`: Unexpected error (`internal`). (`Error`)
- `502`: The engine failed (`upstream_error`). The credits are refunded automatically. (`Error`)
- `504`: The engine timed out (`upstream_timeout`). The credits are refunded automatically. (`Error`)

## Example

```bash
curl -X POST 'https://api.border.bot/v1/calculate/stacking' \
  -H 'Authorization: Bearer bb_live_...' \
  -H 'Content-Type: application/json' \
  -d '{"items":[{"hsCode":"8479.89.94","originCountry":"CN","destinationCountry":"US"}]}'
```