> ## 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.

# Volatility Conversion (Lognormal ↔ Normal)

> Convert between lognormal (Black-Scholes) volatility and normal (Bachelier) volatility. Essential for working across different market conventions.

**Conversion Directions:**
- **lognormal_to_normal**: Convert percentage volatility to absolute volatility
- **normal_to_lognormal**: Convert absolute volatility to percentage volatility

**Use Cases:**
- Reconcile volatility quotes across different market conventions
- Convert historical lognormal vol for use in normal models
- Compare volatility surfaces built with different assumptions
- Switch between model types while maintaining consistency

**Tier:** Standard (2 credits/request) [Tier: PRO, Credits: 5]



## OpenAPI

````yaml api-specs/pricing.json post /quantlib/pricing/bachelier/vol-conversion
openapi: 3.1.0
info:
  title: FinceptQuantLib API - Pricing Module
  description: >-
    Advanced options pricing models including Black-Scholes, Black76, Bachelier,
    Kirk spread options, and binomial trees. Standard Tier access required (2
    credits per request).
  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-pricing
    description: Advanced options pricing models and Greeks calculation
    x-displayName: Pricing
paths:
  /quantlib/pricing/bachelier/vol-conversion:
    post:
      tags:
        - quantlib-pricing
      summary: Volatility Conversion (Lognormal ↔ Normal)
      description: >-
        Convert between lognormal (Black-Scholes) volatility and normal
        (Bachelier) volatility. Essential for working across different market
        conventions.


        **Conversion Directions:**

        - **lognormal_to_normal**: Convert percentage volatility to absolute
        volatility

        - **normal_to_lognormal**: Convert absolute volatility to percentage
        volatility


        **Use Cases:**

        - Reconcile volatility quotes across different market conventions

        - Convert historical lognormal vol for use in normal models

        - Compare volatility surfaces built with different assumptions

        - Switch between model types while maintaining consistency


        **Tier:** Standard (2 credits/request) [Tier: PRO, Credits: 5]
      operationId: bachelier_vol_conversion
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/VolConversionRequest'
            example:
              volatility: 0.25
              forward: 102
              strike: 105
              time_to_maturity: 1
              direction: lognormal_to_normal
      responses:
        '200':
          description: Successful conversion
          content:
            application/json:
              schema:
                type: object
                properties:
                  success:
                    type: boolean
                    example: true
                  data:
                    type: object
                    properties:
                      normal_volatility:
                        type: number
                        description: >-
                          Converted normal volatility (only present for
                          lognormal_to_normal)
                        example: 25.5
                      lognormal_volatility:
                        type: number
                        description: >-
                          Converted lognormal volatility (only present for
                          normal_to_lognormal)
                        example: 0.25
                      direction:
                        type: string
                        description: Conversion direction used
                        example: lognormal_to_normal
        '401':
          $ref: '#/components/responses/UnauthorizedError'
        '402':
          $ref: '#/components/responses/InsufficientCreditsError'
        '422':
          $ref: '#/components/responses/ValidationError'
components:
  schemas:
    VolConversionRequest:
      type: object
      required:
        - volatility
        - forward
        - strike
        - time_to_maturity
      properties:
        volatility:
          type: number
          description: Input volatility to convert (format depends on direction)
          example: 0.25
        forward:
          type: number
          description: Forward price of the underlying asset
          example: 102
        strike:
          type: number
          description: Strike price
          example: 105
        time_to_maturity:
          type: number
          description: Time to expiration in years
          example: 1
        direction:
          type: string
          enum:
            - lognormal_to_normal
            - normal_to_lognormal
          description: Direction of volatility conversion
          example: lognormal_to_normal
          default: lognormal_to_normal
  responses:
    UnauthorizedError:
      description: Authentication information is missing or invalid
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: Invalid API key
    InsufficientCreditsError:
      description: Insufficient API credits for this request
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: >-
                  Insufficient credits. This endpoint costs 2 credits per
                  request.
    ValidationError:
      description: Request validation failed
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: array
                items:
                  type: object
                  properties:
                    loc:
                      type: array
                      items:
                        type: string
                    msg:
                      type: string
                    type:
                      type: string
  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

````