Free calculators
Loan and EMI calculator documentation
Inputs, formulas, assumptions and API/MCP examples for the loan and emi calculator. Reproduce a calculation and cite its sources.
Content updated . Assumptions reviewed .
Formula and assumptions
Reducing payment = P r / (1 - (1+r)^(-n)); flat finance charge = P APR n / 12.
- APR is nominal and divided by 12 for reducing-balance interest.
- Payments occur at month end; interest is retained at full precision until display.
- Flat finance charges are owed in full with no early-settlement rebate; each payment allocates the original principal-to-charge ratio.
- The origination fee is paid upfront and is not financed.
Assumptions reviewed:
Sources
- KlarFort calculator methodology. KlarFort-authored arithmetic; free to use with credit.; vintage 1.
Parameters
| Name | Description | Type | Default | Minimum | Maximum |
|---|---|---|---|---|---|
| currency | Currency | string | "USD" | ||
| principal | Loan principal | number | 20000 | 0 | 1,000,000,000 |
| annualRate | Annual interest rate (%) | number | 6 | 0 | 100 |
| months | Duration in months | integer | 60 | 1 | 600 |
| rateType | Interest calculation | string | "reducing" | ||
| extraMonthly | Extra monthly payment | number | 0 | 0 | 1,000,000,000 |
| lumpSum | One-time extra payment | number | 0 | 0 | 1,000,000,000 |
| lumpSumMonth | Month of one-time payment | integer | 1 | 1 | 600 |
| originationFee | Upfront origination fee | number | 0 | 0 | 1,000,000,000 |
JSON API
GET accepts one input parameter containing URL-encoded JSON. POST sends the JSON input object. Prefer POST for personal figures. Inputs are limited to 16 KiB. POST results are not stored; GET results may be cached for up to 24 hours.
curl -X POST https://klarfort.com/tools/api/v1/loan-calculator -H "Content-Type: application/json" --data '{"currency":"USD","principal":20000,"annualRate":6,"months":60,"rateType":"reducing","extraMonthly":0,"lumpSum":0,"lumpSumMonth":1,"originationFee":0}'fetch("https://klarfort.com/tools/api/v1/loan-calculator", {method:"POST", headers:{"Content-Type":"application/json"}, body:JSON.stringify({"currency":"USD","principal":20000,"annualRate":6,"months":60,"rateType":"reducing","extraMonthly":0,"lumpSum":0,"lumpSumMonth":1,"originationFee":0})})import json, urllib.request
request = urllib.request.Request("https://klarfort.com/tools/api/v1/loan-calculator", data=json.dumps({"currency":"USD","principal":20000,"annualRate":6,"months":60,"rateType":"reducing","extraMonthly":0,"lumpSum":0,"lumpSumMonth":1,"originationFee":0}).encode(), headers={"Content-Type":"application/json"})
print(urllib.request.urlopen(request).read().decode())Connected assistants
Connect using https://klarfort.com/tools/mcp. Discover this calculator with tools/list, then call loan-calculator. Protocol versions 2026-07-28 and 2025-11-25 are supported. Modern requests carry protocol metadata and matching HTTP headers. Set Mcp-Name to params.name for tools/call and to params.uri for resources/read. Older clients initialize first.
Limits: 120 requests per minute per address and approximately 3,000 per minute per edge location. Simulations are capped at 1,000 paths, 600 months and 150,000 path-months (paths multiplied by months). Shorten the duration or reduce paths when that work limit is exceeded. A limit response returns 429 and Retry-After. No exact remaining-request count is available.
Usage and credit
Free for personal, commercial and any other lawful use with credit to KlarFort at https://klarfort.com/. Third-party data terms still apply.
Place a visible credit near the reused material or in the credits for your work or integration. One clear credit per work or integration is sufficient; no separate credit per API request is required. Links to individual calculators are optional.
Computed with KlarFort Calculators, https://klarfort.com/
The API returns this text in credit and the homepage in credit_url. The optional citation_url identifies the calculator for reference. See usage and credit for the full permission.
KlarFort is not financial, investment, tax, or legal advice. Verify outputs before making material decisions.