> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bolta.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Tax Invoice Issuance Deadline

> How to call the API that returns the issuance deadline for a tax invoice write date, and how Bolta sets the deadline.

## What this API returns

`GET /v1/taxInvoiceIssueDueDates` takes a write date and returns the issuance deadline for a tax invoice with that date. The issuance and reverse issuance request APIs already check the write date against the deadline when they receive a request and return `400` if the date is out of range. Call this API when you need the deadline ahead of time, for example to show it in your UI or to check a write date before issuing.

<Info>
  Call this API with an API key alone, without issuer registration, a certificate, or `Bolta-Client-Reference-Id`.
</Info>

You can issue up to and including the deadline.

## Request

| Header          | Required | Description                                                                                    |
| --------------- | -------- | ---------------------------------------------------------------------------------------------- |
| `Authorization` | O        | Set `Basic {apiKey}`. See the [authentication guide](/en/docs/api-introduction/authentication) |

| Query parameter | Required | Description                       |
| --------------- | -------- | --------------------------------- |
| `date`          | O        | Write date in `YYYY-MM-DD` format |

```bash theme={"dark"}
curl "https://xapi.bolta.io/v1/taxInvoiceIssueDueDates?date=YYYY-MM-DD" \
  -H "Authorization: Basic {apiKey}"
```

Replace `YYYY-MM-DD` with the write date you want to check.

Test and live keys return the same result.

## Response

```json theme={"dark"}
{
  "date": "YYYY-MM-DD",
  "issueDueDate": "YYYY-MM-DD"
}
```

| Field          | Type   | Description                              |
| -------------- | ------ | ---------------------------------------- |
| `date`         | string | The write date you requested             |
| `issueDueDate` | string | Issuance deadline in `YYYY-MM-DD` format |

For example, a write date of September 30, 2026 returns an `issueDueDate` of October 12, 2026. October 10 is a Saturday, so the deadline moves to the next business day.

## How the deadline is set

The deadline is the 10th of the month after the write date.

* If the 10th falls on a weekend or public holiday, the deadline is the next business day.
* When the National Tax Service (NTS) extends the deadline for a month, the extended date applies. For write dates in September 2025, the deadline is October 15, 2025.

For a month without a supported deadline, the API returns `400` with `INVALID_REQUEST`.

<Info>
  The API returns the deadline as of the call. Query it again when you need it instead of storing the result long term.
</Info>

## Billing and call quota

This API deducts no points and has no separate call quota. Check your calls in the [Developer Center](https://developers.bolta.io) call logs.

## Errors

| Status code | Error code        | Condition                                                                                                                |
| ----------- | ----------------- | ------------------------------------------------------------------------------------------------------------------------ |
| `400`       | `INVALID_REQUEST` | `date` is missing, is not in `YYYY-MM-DD` format or is not a real date, or falls in a month without a supported deadline |
| `401`       | -                 | API key authentication failed. No response body                                                                          |

For the full list, see [Error Codes](/en/docs/api-introduction/error-codes).

## Related documents

* [Retrieve Tax Invoice Issuance Deadline API](/en/api-reference/tax-invoice-retrieval/retrieve-tax-invoice-issuance-deadline)
* [Email approval reverse issuance](/en/docs/api-introduction/usecase-reverse-email)
* [Simple approval reverse issuance](/en/docs/api-introduction/usecase-reverse-simple)
* [Error Codes](/en/docs/api-introduction/error-codes)