SIBOR 3-Month Loan Cost Comparison: Calculate Your Interest Savings

In the world of finance, understanding interest rates is crucial for making informed borrowing decisions. For businesses and individuals alike, comparing loan costs across different interest rate benchmarks can lead to significant savings. This blog post will explore how to leverage the Interest Rates API to compare the costs of loans based on the 3-month Singapore Interbank Offered Rate (SIBOR) and other relevant benchmarks, such as the US Federal Funds Rate (FED_FUNDS) and the Bank of England Bank Rate (BOE_BANK_RATE).

We will focus on the /convert endpoint of the Interest Rates API, which allows users to compare total interest costs between different rates. This is particularly useful for developers building fintech applications, economists analyzing financial data, and quantitative analysts seeking to optimize loan costs.

Understanding the Interest Rates API

The Interest Rates API provides a comprehensive set of endpoints to access various interest rate data, including central bank rates, interbank rates, and historical time series data. The API is designed to help developers and financial analysts retrieve accurate and up-to-date interest rate information efficiently.

Key features of the Interest Rates API include:

Access to a wide range of interest rate symbols, including FED_FUNDS, ECB_MRO, and BOE_BANK_RATE.
Real-time data retrieval for the latest interest rates.
Historical data access to analyze trends over time.
Comparison of loan costs between different interest rates.

Practical Scenario: Comparing Loan Costs

Imagine a business considering a loan of $100,000 for a term of 12 months. The business wants to compare the total interest costs of borrowing at the current FED_FUNDS rate versus the ECB_MRO and BOE_BANK_RATE. By using the /convert endpoint, the business can quickly determine which option offers the best financial outcome.

Using the /convert Endpoint

The /convert endpoint allows users to compare the total interest cost of a simple loan at the latest rate of each symbol. The required parameters include:

from: The interest rate symbol to compare from (e.g., FED_FUNDS).
to: The interest rate symbol to compare to (e.g., ECB_MRO).
amount: The loan amount (numeric, >= 0).
term_months: The loan term in months (default is 12).

Here’s how to make a request to the /convert endpoint:

curl "https://interestratesapi.com/api/v1/convert?from=FED_FUNDS&to=ECB_MRO&amount=100000&term_months=12&api_key=YOUR_KEY"

The expected JSON response will provide detailed information about the loan costs:


{
"success": true,
"amount": 100000,
"term_months": 12,
"from": {
"symbol": "FED_FUNDS",
"rate": 5.33,
"date": "2026-08-14",
"total_interest": 5330.00,
"total_payment": 105330.00
},
"to": {
"symbol": "ECB_MRO",
"rate": 4.50,
"date": "2026-08-14",
"total_interest": 4500.00,
"total_payment": 104500.00
},
"difference": {
"rate_spread": 0.83,
"interest_saved": 830.00
}
}

Breaking Down the Response Fields

Understanding the response fields is essential for interpreting the results of the loan cost comparison:

success: Indicates whether the API request was successful.
amount: The principal loan amount specified in the request.
term_months: The duration of the loan in months.
from: An object containing details about the loan from the first interest rate symbol:

symbol: The identifier for the interest rate (e.g., FED_FUNDS).
rate: The current interest rate for the symbol.
date: The date of the rate data.
total_interest: The total interest cost for the loan at this rate.
total_payment: The total amount to be paid back, including principal and interest.

to: Similar to the from object, but for the second interest rate symbol (e.g., ECB_MRO).
difference: An object showing the difference between the two rates:

rate_spread: The difference in interest rates between the two symbols.
interest_saved: The amount saved in interest by choosing the lower rate.

Implementing a Reusable Calculator Function

To facilitate loan cost comparisons, we can create a reusable calculator function in both Python and JavaScript. This function will wrap the /convert endpoint and allow users to easily compare loan costs.

Python Implementation

import requests

def compare_loan_costs(from_symbol, to_symbol, amount, term_months, api_key):
response = requests.get(
'https://interestratesapi.com/api/v1/convert',
params=dict(from=from_symbol, to=to_symbol, amount=amount, term_months=term_months, api_key=api_key)
)
data = response.json()
return data

JavaScript Implementation

async function compareLoanCosts(fromSymbol, toSymbol, amount, termMonths, apiKey) {
const response = await fetch(
`https://interestratesapi.com/api/v1/convert?from=${fromSymbol}&to=${toSymbol}&amount=${amount}&term_months=${termMonths}&api_key=${apiKey}`
);
const data = await response.json();
return data;
}

Current FED_FUNDS Rate and Contextualization

To provide context for our comparisons, we can retrieve the latest FED_FUNDS rate using the /latest endpoint. This will allow us to understand the current borrowing environment:

curl "https://interestratesapi.com/api/v1/latest?symbols=FED_FUNDS&api_key=YOUR_KEY"

The expected JSON response will look like this:


{
"success": true,
"date": "2026-08-14",
"base": "MIXED",
"rates": {
"FED_FUNDS": 5.33
},
"currencies": {
"FED_FUNDS": "USD"
}
}

By integrating the latest FED_FUNDS rate into our loan cost comparisons, we can ensure that our calculations reflect the most current financial conditions.

Use Cases for the Interest Rates API

The Interest Rates API can be utilized in various applications, including:

Mortgage Comparison Tools: Help users find the best mortgage rates by comparing different loan options.
Interbank Lending Cost Analysis: Financial institutions can analyze the costs associated with lending to each other based on current interbank rates.
Fintech Lending Applications: Developers can build applications that provide users with real-time loan cost comparisons, enhancing decision-making.

Conclusion

In conclusion, the Interest Rates API provides a powerful tool for comparing loan costs across different interest rate benchmarks. By utilizing the /convert endpoint, developers and financial analysts can make informed decisions that lead to significant interest savings. Whether you are building a mortgage comparison tool or analyzing interbank lending costs, the Interest Rates API offers the data and functionality needed to succeed in today's financial landscape.

To get started with the Interest Rates API, visit Get started with Interest Rates API and explore the various features available to enhance your financial applications.