> ## 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 Par Swap Rate

> Calculate the par swap rate (also known as the swap rate) from a set of discount factors. The par rate is the fixed rate that makes the present value of fixed-leg payments equal to the present value of floating-leg payments at inception. This is the market convention for quoting interest rate swaps and is a key input for swap curve construction and valuation. [Tier: STANDARD, Credits: 2]



## OpenAPI

````yaml api-specs/solver.json post /quantlib/solver/finance/par-rate
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/par-rate:
    post:
      tags:
        - quantlib-solver
      summary: Calculate Par Swap Rate
      description: >-
        Calculate the par swap rate (also known as the swap rate) from a set of
        discount factors. The par rate is the fixed rate that makes the present
        value of fixed-leg payments equal to the present value of floating-leg
        payments at inception. This is the market convention for quoting
        interest rate swaps and is a key input for swap curve construction and
        valuation. [Tier: STANDARD, Credits: 2]
      operationId: par_rate
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - discount_factors
                - times
              properties:
                discount_factors:
                  type: array
                  description: Array of discount factors at each payment time
                  items:
                    type: number
                  example:
                    - 0.98
                    - 0.96
                    - 0.94
                    - 0.92
                    - 0.9
                times:
                  type: array
                  description: Array of payment times in years
                  items:
                    type: number
                  example:
                    - 0.5
                    - 1
                    - 1.5
                    - 2
                    - 2.5
                frequency:
                  type: integer
                  description: Payment frequency per year
                  default: 2
                  enum:
                    - 1
                    - 2
                    - 4
                    - 12
                  example: 2
            example:
              discount_factors:
                - 0.98
                - 0.96
                - 0.94
                - 0.92
                - 0.9
              times:
                - 0.5
                - 1
                - 1.5
                - 2
                - 2.5
              frequency: 2
      responses:
        '200':
          description: Successful Response
          content:
            application/json:
              schema:
                type: object
                properties:
                  success:
                    type: boolean
                    example: true
                  data:
                    type: object
                    properties:
                      par_rate:
                        type: number
                        description: The calculated par swap rate as a decimal
                        example: 0.0427
              example:
                success: true
                data:
                  par_rate: 0.0427
        '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

````