Calculate blended interest rate across multiple loans
A first mortgage of 240,000 at 6.5%, a piggyback loan of 60,000 at 9.25% and 25,000 at 4.75% blend into one rate of just under 7% on 325,000. Each rate counts in proportion to its balance. Free in your browser.
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Run — free
This blended interest rate calculator combines two or more loans into one balance-weighted annual rate. Enter each outstanding balance and its interest rate as a percentage, and the calculator reports the single rate that represents the portfolio as a whole. It is useful for reviewing a first mortgage with a piggyback loan, comparing existing debts with a refinance proposal, or summarizing several business loans without giving a small balance the same influence as a large one.
Why a balance-weighted rate is the meaningful comparison
A simple average treats every loan as equally important, even when their balances are very different. That can give a misleading picture of the cost of borrowing. Suppose one loan carries most of the debt at a moderate rate while a much smaller second loan has a higher rate.
Adding the two rates and dividing by two exaggerates the influence of the smaller loan. This calculator instead multiplies each annual percentage rate by its current balance, adds those weighted amounts, and divides the result by the combined balance. The resulting blended interest rate is the rate that would produce the same annual interest amount if the full balance were represented as one loan, assuming balances stayed unchanged.
Enter rates as percentages, so a rate of six and one-half percent is entered as 6.5, not 0.065. Use the same currency for every balance. Currency symbols are unnecessary because the calculation depends on proportions, but mixing dollars, euros, or other currencies without conversion would make those proportions meaningless.
At least two loans are required, and their total balance must be greater than zero.
How to read and verify the result
The primary result is the blended annual interest rate expressed as a percentage. It must normally fall between the lowest and highest rates among loans that have positive balances. A zero-balance loan has no effect because its weight is zero, although it remains part of the submitted loan count.
The response also returns the combined balance and the number of loan records, making it easier to confirm that the intended portfolio was included. For a quick independent check, calculate each loan's approximate annual interest by multiplying its balance by its percentage rate and dividing by one hundred. Add those interest amounts, divide by the total balance, and multiply by one hundred.
Small differences may arise only from display rounding. This is a nominal blended rate, not an annual percentage rate that incorporates fees, points, compounding conventions, mortgage insurance, or closing costs. It also does not forecast amortization.
Because balances change as payments are made, the blended rate describes the balances entered now. Recalculate it whenever balances or contractual rates change if you need an updated portfolio view.
Using the calculation for refinancing and debt decisions
A blended rate provides a clean starting point when comparing several current loans with one proposed replacement loan. If the proposed rate is below the current blended rate, its interest rate alone is lower on the same principal, but that does not automatically make refinancing beneficial. Include origination charges, prepayment penalties, taxes, insurance changes, the new repayment term, and any cash added to the balance before deciding.
Extending the term can reduce a monthly payment while increasing total interest paid. The calculation is also helpful when a property purchase uses a primary mortgage and a smaller piggyback loan. It shows the combined rate without pretending that both liens have equal weight.
Businesses can use the same method to summarize multiple credit facilities, and households can use it to establish a baseline before prioritizing repayment. When evaluating which loan to pay down first, remember that the blended rate describes the portfolio rather than prescribing a strategy. Paying extra toward a high-rate loan generally changes the blend differently from paying the same amount toward a low-rate loan.
Re-enter the projected balances to model that change, while treating tax and legal consequences separately.
What you can do with it
Combine a mortgage and piggyback loan
Find one balance-weighted rate for a primary mortgage and a smaller second lien without letting the smaller loan count equally.
Evaluate a refinance quote
Compare a proposed replacement rate with the blended rate of the loans that would be paid off, then assess fees and term changes separately.
Summarize a debt portfolio
Report a representative interest rate for several household or business loans while preserving each balance's true influence.
FAQ
What does the calculation cost?
The calculation can also run in the browser.
Why not take the ordinary average of the rates?
An ordinary average gives a small loan the same influence as a large loan. Weighting by balance reflects each loan's contribution to the combined borrowing cost.
Does the blended rate include fees or closing costs?
No. It combines stated interest rates only. It is not an APR calculation and does not include points, fees, insurance, or other charges.
Can balances use different currencies?
No. Convert every balance to one currency first so their relative weights are meaningful.
How can I check the blended rate by hand?
Multiply each balance by its rate and divide by 100 to get each loan's yearly interest. Add those amounts, divide by the total balance and multiply by 100. Only display rounding can make the two results differ slightly.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/fin/piggyback-loan-combined-rate \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"loans":[{"balance":240000,"interest_rate":6.5},{"balance":60000,"interest_rate":9.25}]}'const res = await fetch("https://api.kit.forhosting.com/fin/piggyback-loan-combined-rate", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"loans": [
{
"balance": 240000,
"interest_rate": 6.5
},
{
"balance": 60000,
"interest_rate": 9.25
}
]
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/fin/piggyback-loan-combined-rate",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"loans": [
{
"balance": 240000,
"interest_rate": 6.5
},
{
"balance": 60000,
"interest_rate": 9.25
}
]
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/fin/piggyback-loan-combined-rate", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"loans":[{"balance":240000,"interest_rate":6.5},{"balance":60000,"interest_rate":9.25}]}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"loans":[{"balance":240000,"interest_rate":6.5},{"balance":60000,"interest_rate":9.25}]}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/fin/piggyback-loan-combined-rate", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"loans": [
{
"balance": 240000,
"interest_rate": 6.5
},
{
"balance": 60000,
"interest_rate": 9.25
}
]
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "fin.piggyback_loan_combined_rate",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_items | 1000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical questions
Should I enter 6.5 or 0.065 for a 6.5% rate?
Enter 6.5. Every interest_rate value is interpreted as a percentage.
What happens when every balance is zero?
The request returns an invalid_input error because a weighted rate is undefined when the total balance is zero.