How to Integrate US Treasury 3-Month Data into Your App: Complete API Guide

Introduction

In the world of finance, access to accurate and timely interest rate data is crucial for developers, economists, and financial analysts. The US Treasury 3-Month yield is a key indicator of short-term interest rates and is widely used in financial modeling, risk assessment, and investment strategies. Integrating this data into your application can enhance its functionality and provide valuable insights to users. This blog post serves as a comprehensive guide on how to integrate US Treasury 3-Month data into your application using the Interest Rates API from interestratesapi.com.

Understanding the Interest Rates API

The Interest Rates API provides a robust set of endpoints to access various interest rate data, including central bank rates, interbank rates, and treasury rates. For our purposes, we will focus on the US Treasury 3-Month yield, identified by the symbol US_TREASURY_3M. This API allows developers to retrieve the latest rates, historical data, time series, and more, all through simple GET requests.

API Endpoints Overview

The Interest Rates API offers several endpoints that we will utilize in our integration:

/symbols - Retrieve a catalogue of available rate symbols.
/latest - Get the latest value for specified symbols.
/historical - Fetch the value of a symbol on a specific date.
/timeseries - Obtain a series of values between two dates.
/fluctuation - Analyze change statistics over a range.
/ohlc - Get OHLC candlestick data.
/convert - Compare loan interest costs between two rates.

Step 1: Retrieve Available Symbols

Before making any requests for interest rate data, it’s essential to know the available symbols. The first step is to call the /symbols endpoint.

cURL Example

curl "https://interestratesapi.com/api/v1/symbols?category=treasury&base=USD&api_key=YOUR_KEY"

Python Example

import requests

response = requests.get(
'https://interestratesapi.com/api/v1/symbols',
params=dict(category='treasury', base='USD', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/symbols?category=treasury&base=USD&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/symbols?category=treasury&base=USD&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"count": 1,
"symbols": [
{
"symbol": "US_TREASURY_3M",
"name": "US Treasury Yield 3-Month",
"category": "treasury",
"country_code": "US",
"currency_code": "USD",
"frequency": "daily",
"description": "The interest rate on US Treasury bills maturing in 3 months."
}
]
}

Step 2: Fetch the Latest US Treasury 3-Month Rate

Once you have confirmed the availability of the US_TREASURY_3M symbol, the next step is to retrieve the latest rate using the /latest endpoint.

cURL Example

curl "https://interestratesapi.com/api/v1/latest?symbols=US_TREASURY_3M&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/latest',
params=dict(symbols='US_TREASURY_3M', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/latest?symbols=US_TREASURY_3M&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/latest?symbols=US_TREASURY_3M&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"date": "2026-06-29",
"base": "USD",
"rates": {
"US_TREASURY_3M": 5.33
},
"dates": {
"US_TREASURY_3M": "2026-06-29"
},
"currencies": {
"US_TREASURY_3M": "USD"
}
}

Step 3: Retrieve Historical Data

To analyze trends over time, you may want to fetch historical data for the US Treasury 3-Month yield. This can be done using the /historical endpoint.

cURL Example

curl "https://interestratesapi.com/api/v1/historical?date=2025-06-15&symbols=US_TREASURY_3M&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/historical',
params=dict(date='2025-06-15', symbols='US_TREASURY_3M', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/historical?date=2025-06-15&symbols=US_TREASURY_3M&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/historical?date=2025-06-15&symbols=US_TREASURY_3M&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"date": "2025-06-15",
"base": "USD",
"rates": {
"US_TREASURY_3M": 5.33
},
"currencies": {
"US_TREASURY_3M": "USD"
}
}

Step 4: Analyze Time Series Data

For a more comprehensive analysis, you can retrieve a time series of rates between two dates using the /timeseries endpoint.

cURL Example

curl "https://interestratesapi.com/api/v1/timeseries?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/timeseries',
params=dict(start='2025-06-29', end='2026-06-29', symbols='US_TREASURY_3M', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/timeseries?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/timeseries?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"base": "USD",
"start_date": "2025-06-29",
"end_date": "2026-06-29",
"rates": {
"US_TREASURY_3M": {
"2025-01-02": 5.33,
"2025-01-03": 5.33,
"2025-01-06": 5.33
}
},
"frequencies": {
"US_TREASURY_3M": "daily"
},
"currencies": {
"US_TREASURY_3M": "USD"
}
}

Step 5: Analyze Fluctuations

Understanding how rates fluctuate over time can provide insights into market trends. The /fluctuation endpoint allows you to analyze change statistics over a specified date range.

cURL Example

curl "https://interestratesapi.com/api/v1/fluctuation?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/fluctuation',
params=dict(start='2025-06-29', end='2026-06-29', symbols='US_TREASURY_3M', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/fluctuation?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/fluctuation?start=2025-06-29&end=2026-06-29&symbols=US_TREASURY_3M&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"rates": {
"US_TREASURY_3M": {
"start_date": "2025-06-29",
"end_date": "2026-06-29",
"start_value": 5.50,
"end_value": 5.33,
"change": -0.17,
"change_pct": -3.09,
"high": 5.50,
"low": 5.25
}
}
}

Step 6: Retrieve OHLC Data

For applications that require candlestick data, the /ohlc endpoint provides open, high, low, and close values for the US Treasury 3-Month yield.

cURL Example

curl "https://interestratesapi.com/api/v1/ohlc?symbols=US_TREASURY_3M&period=monthly&start=2025-06-29&end=2026-06-29&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/ohlc',
params=dict(symbols='US_TREASURY_3M', period='monthly', start='2025-06-29', end='2026-06-29', api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/ohlc?symbols=US_TREASURY_3M&period=monthly&start=2025-06-29&end=2026-06-29&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/ohlc?symbols=US_TREASURY_3M&period=monthly&start=2025-06-29&end=2026-06-29&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"period": "monthly",
"start_date": "2025-06-29",
"end_date": "2026-06-29",
"rates": {
"US_TREASURY_3M": [
{
"period": "2025-01",
"open": 5.50,
"high": 5.50,
"low": 5.33,
"close": 5.33,
"data_points": 23
}
]
}
}

Step 7: Compare Loan Interest Costs

Finally, you can use the /convert endpoint to compare the total interest cost of a loan between two rates. This is particularly useful for financial applications that help users make informed borrowing decisions.

cURL Example

curl "https://interestratesapi.com/api/v1/convert?from=US_TREASURY_3M&to=ECB_MRO&amount=100000&term_months=12&api_key=YOUR_KEY"

Python Example

response = requests.get(
'https://interestratesapi.com/api/v1/convert',
params=dict(from='US_TREASURY_3M', to='ECB_MRO', amount=100000, term_months=12, api_key='YOUR_KEY')
)
data = response.json()

JavaScript Example

const response = await fetch(
'https://interestratesapi.com/api/v1/convert?from=US_TREASURY_3M&to=ECB_MRO&amount=100000&term_months=12&api_key=YOUR_KEY'
);
const data = await response.json();

PHP Example

<?php

$response = file_get_contents('https://interestratesapi.com/api/v1/convert?from=US_TREASURY_3M&to=ECB_MRO&amount=100000&term_months=12&api_key=YOUR_KEY');
$data = json_decode($response, true);

Expected JSON Response

{
"success": true,
"amount": 100000,
"term_months": 12,
"from": {
"symbol": "US_TREASURY_3M",
"rate": 5.33,
"date": "2026-06-29",
"total_interest": 5330.00,
"total_payment": 105330.00
},
"to": {
"symbol": "ECB_MRO",
"rate": 4.50,
"date": "2026-06-29",
"total_interest": 4500.00,
"total_payment": 104500.00
},
"difference": {
"rate_spread": 0.83,
"interest_saved": 830.00
}
}

Error Handling

When integrating with the Interest Rates API, it's essential to handle potential errors gracefully. Here are some common error responses you may encounter:

401: Missing or invalid API key.
403: Account without an active plan.
404: No symbols matched or no data for the requested date/range.
422: Validation error (e.g., wrong date format, invalid symbol).
429: Request quota exhausted.

For each of these errors, you should implement appropriate error handling in your application to inform users and possibly retry the request after a delay.

Understanding Rate Limit Headers

The Interest Rates API provides rate limit headers in the response, which can help you manage your API usage effectively:

X-RateLimit-Limit: The maximum number of requests allowed in a given time period.
X-RateLimit-Remaining: The number of requests remaining in the current time period.
X-RateLimit-Reset: The time when the rate limit will reset.

Monitoring these headers can help you avoid hitting rate limits and ensure a smooth user experience.

Mini Project: Node.js/Express Endpoint

To demonstrate the integration of the US Treasury 3-Month data, let's create a simple Node.js/Express endpoint that fetches, caches, and serves the latest rate data.

const express = require('express');
const axios = require('axios');
const app = express();
const PORT = process.env.PORT || 3000;

let cachedRate = null;

app.get('/api/us-treasury-3m', async (req, res) => {
if (cachedRate) {
return res.json(cachedRate);
}

try {
const response = await axios.get('https://interestratesapi.com/api/v1/latest', {
params: {
symbols: 'US_TREASURY_3M',
api_key: 'YOUR_KEY'
}
});
cachedRate = response.data;
res.json(cachedRate);
} catch (error) {
res.status(500).json({ error: 'Failed to fetch data' });
}
});

app.listen(PORT, () => {
console.log(`Server is running on port ${PORT}`);
});

Conclusion

Integrating US Treasury 3-Month data into your application using the Interest Rates API from interestratesapi.com is a straightforward process that can significantly enhance your application's financial capabilities. By following the steps outlined in this guide, you can access a wealth of interest rate data, analyze trends, and provide valuable insights to your users. Whether you are building a fintech application, conducting economic research, or developing financial models, the Interest Rates API is an invaluable resource.

For more information and to explore additional features, visit Explore Interest Rates API features and Get started with Interest Rates API.

Introduction

Understanding the Interest Rates API

API Endpoints Overview

Step 1: Retrieve Available Symbols

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 2: Fetch the Latest US Treasury 3-Month Rate

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 3: Retrieve Historical Data

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 4: Analyze Time Series Data

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 5: Analyze Fluctuations

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 6: Retrieve OHLC Data

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Step 7: Compare Loan Interest Costs

cURL Example

Python Example

JavaScript Example

PHP Example

Expected JSON Response

Error Handling

Understanding Rate Limit Headers

Mini Project: Node.js/Express Endpoint

Conclusion

Ready to get started?

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