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

# Calculate Z-Spread

> Calculate the Z-spread (Zero-volatility spread) - the constant spread that, when added to the spot rate curve, makes the present value of a bond's cash flows equal its market price. Unlike G-spread or I-spread which compare yields, Z-spread properly accounts for the term structure of interest rates by discounting each cash flow at the appropriate spot rate plus spread. This provides a more accurate measure of credit risk. Essential for relative value analysis and credit trading. [Tier: STANDARD, Credits: 2]



## OpenAPI

````yaml api-specs/solver.json post /quantlib/solver/finance/z-spread
openapi: 3.1.0
info:
  title: FinceptQuantLib API - Solver
  description: >-
    Solver module endpoints for FinceptQuantLib API. The Solver module (Basic
    Tier, 1 credit per request) provides advanced financial solvers including
    bond analytics (yield, duration, convexity), implied volatility
    calculations, spread computations (Z-spread, ASW, OAS), curve bootstrapping,
    interest rate conversions, and model calibration (Vasicek, CIR). Essential
    for fixed income analysis, derivatives pricing, and risk management.
  version: 3.0.0
  contact:
    name: Fincept API Support
    url: https://fincept.in
servers:
  - url: https://api.fincept.in
    description: Fincept API Production Server
security:
  - APIKeyHeader: []
tags:
  - name: quantlib-solver
    description: >-
      Advanced financial solvers for bond analytics, implied volatility, spread
      calculations, and model calibration
    x-displayName: Solver
paths:
  /quantlib/solver/finance/z-spread:
    post:
      tags:
        - quantlib-solver
      summary: Calculate Z-Spread
      description: >-
        Calculate the Z-spread (Zero-volatility spread) - the constant spread
        that, when added to the spot rate curve, makes the present value of a
        bond's cash flows equal its market price. Unlike G-spread or I-spread
        which compare yields, Z-spread properly accounts for the term structure
        of interest rates by discounting each cash flow at the appropriate spot
        rate plus spread. This provides a more accurate measure of credit risk.
        Essential for relative value analysis and credit trading. [Tier:
        STANDARD, Credits: 2]
      operationId: z_spread
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - price
                - cashflows
                - times
                - base_rates
              properties:
                price:
                  type: number
                  description: Current market price of the bond
                  example: 98.5
                cashflows:
                  type: array
                  description: Array of bond cash flows (coupons and principal)
                  items:
                    type: number
                  example:
                    - 2.5
                    - 2.5
                    - 2.5
                    - 2.5
                    - 102.5
                times:
                  type: array
                  description: Array of payment times in years
                  items:
                    type: number
                  example:
                    - 0.5
                    - 1
                    - 1.5
                    - 2
                    - 2.5
                base_rates:
                  type: array
                  description: >-
                    Array of zero rates (spot rates) at each payment time as
                    decimals
                  items:
                    type: number
                  example:
                    - 0.03
                    - 0.032
                    - 0.034
                    - 0.036
                    - 0.038
            example:
              price: 98.5
              cashflows:
                - 2.5
                - 2.5
                - 2.5
                - 2.5
                - 102.5
              times:
                - 0.5
                - 1
                - 1.5
                - 2
                - 2.5
              base_rates:
                - 0.03
                - 0.032
                - 0.034
                - 0.036
                - 0.038
      responses:
        '200':
          description: Successful Response
          content:
            application/json:
              schema:
                type: object
                properties:
                  success:
                    type: boolean
                    example: true
                  data:
                    type: object
                    properties:
                      z_spread:
                        type: number
                        description: >-
                          The Z-spread as a decimal (multiply by 10000 for basis
                          points)
                        example: 0.0125
              example:
                success: true
                data:
                  z_spread: 0.0125
        '401':
          $ref: '#/components/responses/UnauthorizedError'
        '402':
          $ref: '#/components/responses/InsufficientTierError'
        '422':
          description: Validation Error
          content:
            application/json:
              schema:
                type: object
                properties:
                  detail:
                    type: array
                    items:
                      type: object
      security:
        - APIKeyHeader: []
components:
  responses:
    UnauthorizedError:
      description: Authentication information is missing or invalid
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: Invalid API key
    InsufficientTierError:
      description: API tier insufficient for this endpoint
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: Endpoint requires Basic tier or higher
  securitySchemes:
    APIKeyHeader:
      type: apiKey
      in: header
      name: X-API-Key
      description: >-
        API key for authentication. Get your key at
        https://api.fincept.in/auth/register

````