Developer API — Coming Soon

The Financial Calculator API for Developers

A single, clean REST API for 125+ financial calculations. Mortgage payments, compound interest, retirement projections, tax estimates — all returning structured JSON. No math required.

Request API Access View Endpoints

125+

Calculators

REST

JSON API

<50ms

Response Time

Authentication

All API requests require a Bearer token in the Authorization header. API keys are issued per-application and available through your dashboard.

RESTJSONHTTPSBearer Auth

# Base URL

https://api.calcfi.app

# Authentication

Authorization: Bearer YOUR_API_KEY

Content-Type: application/json

API Reference

Every endpoint accepts JSON and returns structured results.

POST

/v1/calculate/mortgage

Calculate monthly mortgage payment, total interest, and amortization schedule.

Parameters

Name	Type	Required	Description
principal	number	required	Loan amount in USD
annual_rate	number	required	Annual interest rate as a decimal (e.g. 0.065)
term_years	integer	required	Loan term in years (e.g. 30)
include_amortization	boolean	optional	Return full amortization schedule

Request Body

{
  "principal": 400000,
  "annual_rate": 0.065,
  "term_years": 30,
  "include_amortization": false
}

Response

{
  "monthly_payment": 2528.27,
  "total_interest": 510178.20,
  "total_cost": 910178.20,
  "payoff_date": "2055-04-01",
  "meta": {
    "calculator": "mortgage",
    "version": "1.0",
    "computed_at": "2025-04-01T12:00:00Z"
  }
}

POST

/v1/calculate/compound-interest

Calculate compound interest growth with optional regular contributions.

Parameters

Name	Type	Required	Description
principal	number	required	Initial investment amount
annual_rate	number	required	Annual interest rate as a decimal
years	integer	required	Investment duration in years
monthly_contribution	number	optional	Regular monthly contribution
compound_frequency	string	optional	"monthly" \| "quarterly" \| "annually"

Request Body

{
  "principal": 10000,
  "annual_rate": 0.07,
  "years": 30,
  "monthly_contribution": 500,
  "compound_frequency": "monthly"
}

Response

{
  "final_value": 613089.34,
  "total_contributions": 190000.00,
  "total_interest_earned": 423089.34,
  "growth_multiple": 3.23,
  "yearly_breakdown": [
    { "year": 1, "value": 17283.40 },
    { "year": 5, "value": 51640.28 }
  ]
}

POST

/v1/calculate/retirement

Project retirement savings and determine required monthly contribution to reach a goal.

Parameters

Name	Type	Required	Description
current_age	integer	required	Current age in years
retirement_age	integer	required	Target retirement age
current_savings	number	required	Current retirement savings balance
monthly_contribution	number	required	Current monthly contribution
annual_return	number	optional	Expected annual return (default 0.07)

Request Body

{
  "current_age": 35,
  "retirement_age": 65,
  "current_savings": 50000,
  "monthly_contribution": 1000,
  "annual_return": 0.07
}

Response

{
  "projected_balance": 1247892.50,
  "years_to_retirement": 30,
  "monthly_income_at_4pct": 4159.64,
  "on_track": true,
  "required_monthly_for_1m": 831.52,
  "required_monthly_for_2m": 1663.04
}

GET

/v1/calculators

List all available calculators with their slugs, categories, and required parameters.

Parameters

Name	Type	Required	Description
category	string	optional	Filter by category (e.g. "mortgage", "retirement", "tax")

Request

GET /v1/calculators?category=mortgage
Authorization: Bearer YOUR_API_KEY

Response

{
  "calculators": [
    {
      "slug": "mortgage-payment",
      "name": "Mortgage Payment Calculator",
      "category": "mortgage",
      "endpoint": "/v1/calculate/mortgage"
    },
    {
      "slug": "mortgage-affordability",
      "name": "Mortgage Affordability Calculator",
      "category": "mortgage",
      "endpoint": "/v1/calculate/mortgage-affordability"
    }
  ],
  "total": 14,
  "categories": ["mortgage", "retirement", "investing", "debt", "tax", "business"]
}

Error Handling

400

Bad Request

Missing or invalid parameters. Check the error.details field for specifics.

401

Unauthorized

Missing or invalid API key. Include a valid Bearer token.

404

Not Found

The requested calculator endpoint doesn't exist. Use GET /v1/calculators to list available endpoints.

429

Rate Limited

Too many requests. Default limits are 100 req/min on free tier, 1000/min on paid plans.

422

Unprocessable

Parameters are present but values are out of valid range (e.g. negative interest rate).

500

Server Error

Internal error. These are rare and monitored. Retry with exponential backoff.

Who Uses the CalcFi API

Built for developers who need accurate financial calculations without reinventing the math.

🏦

Fintech Apps

Add financial planning tools to your banking or investment app without building from scratch.

📊

Robo-Advisors

Power retirement projections and investment calculators in automated advisory platforms.

🏠

Real Estate Platforms

Integrate mortgage, affordability, and rent-vs-buy calculations into property listings.

📱

Mobile Apps

Fetch calculation results server-side and display them natively in iOS and Android apps.

📰

Publisher Tools

Build custom interactive widgets that pull live calculations for editorial content.

🤖

AI Assistants

Give your LLM-powered financial assistant accurate, structured calculation capabilities.

Why CalcFi API

Sub-50ms responses

Calculations are pure math — no database lookups. Responses are fast enough for real-time UIs.

Simple REST API

Standard JSON in, JSON out. No proprietary SDKs or query languages to learn.

Always up-to-date

Tax brackets, IRS limits, and rate tables are maintained by CalcFi. You get correct results without maintaining data.

125+ calculators

Mortgage, compound interest, retirement, income tax, Social Security, crypto, and 100+ more.

Structured output

Consistent, typed JSON responses. Predictable field names. Easy to integrate and parse.

Scales with you

From prototype to production. Rate limits that grow with your plan. No vendor lock-in.

Pricing (Coming Soon)

Early access users on the waitlist will receive discounted pricing.

Starter

Freeforever

✓ 1,000 requests/month
✓ All 125+ calculators
✓ REST API access
✓ Community support

Join Waitlist

Pro

$29/month

✓ 50,000 requests/month
✓ All calculators
✓ Priority support
✓ Webhook callbacks
✓ Higher rate limits

Join Waitlist

Enterprise

Custompricing

✓ Unlimited requests
✓ SLA guarantee
✓ Dedicated support
✓ Custom calculators
✓ On-premise option

🚀 Early Access

Request API Access

The CalcFi API is in development. Join the waitlist to get early access, shape the feature set, and receive launch pricing.

No spam. You'll only hear from us when the API launches.

FAQ

When will the API launch?

We're actively building it. Waitlist members will get early access and will be notified before public launch. Join above.

Will there be a free tier?

Yes. We plan to offer a free Starter tier with 1,000 requests/month to let developers prototype and build without upfront commitment.

Can I use the embed iframes right now?

Absolutely. While the API is in development, you can embed any CalcFi calculator on your website for free right now via the /embed page. No API key required.

Which calculators will be available?

All 125+ CalcFi calculators. That includes mortgage, compound interest, retirement, taxes, debt payoff, crypto, business, salary, and more.

Will you build custom calculators?

Enterprise plans will include custom calculator development. If you have a specific calculation need, mention it in the waitlist form.

Want to use CalcFi right now?

While the API is in development, you can embed any calculator on your website for free today.

Get Free Embed Code