> ## 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. # Retrieve Tax Invoice Issuance Deadline > Send a write date and the API returns the issuance deadline for a tax invoice with that date. You can issue up to and including the deadline; from the next day on, Bolta does not accept the issuance. The issuance and reverse issuance request APIs already check the deadline on each request, so call this API when you need the deadline ahead of time. You need no registered issuer, certificate, or client reference ID. Test and live keys return the same result, and the call deducts no points. The deadline is the 10th of the month after the write date. If the 10th falls on a weekend or public holiday, the deadline moves to the next business day. When the NTS extends the deadline for a month, the extended date applies. Bolta updates its servers when a new public holiday is declared or the NTS extends a deadline, so query the deadline when you need it instead of storing the result. The API only answers for months whose deadlines Bolta maintains and rejects other months with `400`. [Tax invoice issuance deadline guide](/en/api-introduction/tax-invoice-issue-due-date) ## OpenAPI ````yaml /openapi.en.yaml get /v1/taxInvoiceIssueDueDates openapi: 3.1.0 info: title: Bolta API description: > The Bolta e-tax invoice API. [API Overview](/en/api-introduction/overview) | [Authentication guide](/en/api-introduction/authentication) | [Use cases](/en/api-introduction/usecase-b2b) version: 1.0.0 servers: - url: https://xapi.bolta.io description: Bolta API server security: - basicAuth: [] tags: - name: Tax Invoice Issuance description: > Issue and amend e-tax invoices. [Calculating the issuance amount](/en/api-introduction/issuance-guide) | [Amendment types](/en/api-introduction/amendment-guide) - name: Tax Invoice Retrieval description: Retrieve e-tax invoice results and request processing status. - name: Reverse Issuance description: > Request and manage reverse issuance of e-tax invoices. [Email-approval reverse issuance](/en/api-introduction/usecase-reverse-email) | [Simple-approval reverse issuance](/en/api-introduction/usecase-reverse-simple) - name: Cash Receipt description: > Issue, cancel, and check the status of cash receipts. Check the final result via webhook or the status API. A live request that remains in progress or needs its issuance result confirmed can be finalized after 17:00 KST on the day following the request. [Cash receipt guide](/en/api-introduction/cash-receipt-guide) | [Cash receipt webhooks](/en/api-introduction/webhook-cash-receipt) - name: Business Registration Status description: > Check the registration status and tax type of a business registration number. Look up one number or up to 100 numbers at once. This API requires no issuer registration and no certificate. [Business registration status guide](/en/api-introduction/business-registration-status) - name: Issuer description: > Register and manage businesses that act as tax invoice issuers. Certificate requirements depend on the issuance type. [Glossary](/en/api-introduction/glossary) | [Delegated issuance](/en/api-introduction/usecase-delegated) | [Brokered Tax Invoice Issuance](/en/api-introduction/usecase-brokered) - name: Certificate description: > Register and manage issuer certificates. [Certificate registration](/en/api-introduction/certificate-registration) paths: /v1/taxInvoiceIssueDueDates: get: tags: - Tax Invoice Retrieval summary: Retrieve Tax Invoice Issuance Deadline description: > Send a write date and the API returns the issuance deadline for a tax invoice with that date. You can issue up to and including the deadline; from the next day on, Bolta does not accept the issuance. The issuance and reverse issuance request APIs already check the deadline on each request, so call this API when you need the deadline ahead of time. You need no registered issuer, certificate, or client reference ID. Test and live keys return the same result, and the call deducts no points. The deadline is the 10th of the month after the write date. If the 10th falls on a weekend or public holiday, the deadline moves to the next business day. When the NTS extends the deadline for a month, the extended date applies. Bolta updates its servers when a new public holiday is declared or the NTS extends a deadline, so query the deadline when you need it instead of storing the result. The API only answers for months whose deadlines Bolta maintains and rejects other months with `400`. [Tax invoice issuance deadline guide](/en/api-introduction/tax-invoice-issue-due-date) parameters: - name: date in: query description: Write date. Use the `YYYY-MM-DD` format. required: true example: '2026-09-30' schema: type: string format: date responses: '200': description: Lookup succeeded content: application/json: schema: $ref: '#/components/schemas/TaxInvoiceIssueDueDateResponse' examples: The 10th falls on a weekend: x-parity-id: weekend-shift summary: >- The 10th is a Saturday, so the deadline moves to the next business day value: date: '2026-09-30' issueDueDate: '2026-10-12' The NTS extended the deadline: x-parity-id: nts-extension summary: The deadline follows the NTS extension value: date: '2025-09-01' issueDueDate: '2025-10-15' headers: {} '400': description: > `date` is missing or is not a real date in `YYYY-MM-DD` format. A month for which Bolta does not provide a deadline returns the same response. The response `code` is `INVALID_REQUEST`. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '401': description: API key authentication failed. The response has no body. deprecated: false components: schemas: TaxInvoiceIssueDueDateResponse: type: object description: Tax invoice issuance deadline lookup result properties: date: type: string format: date description: The write date you requested issueDueDate: type: string format: date description: Issuance deadline. Issuing on or before this date is on time. required: - date - issueDueDate ErrorResponse: type: object description: The error response returned when an API request fails properties: code: type: string description: Error type identifier message: type: string description: Error description traceId: type: string description: Request trace identifier required: - code - message - traceId securitySchemes: basicAuth: type: http scheme: basic description: >- Base64-encode your API key and pass it. Enter the API key as the username and leave the password empty. ````