Free Blended Rate Calculator

Understanding the Blended Rate and Its Calculation

The blended rate—also known as the weighted average interest rate, blended APR, or combined loan rate—is a single effective interest rate that reflects the true cost of carrying multiple debts, loans, or mortgages simultaneously. This Blended Rate Calculator (a free weighted average interest rate tool available online) enables you to quickly compute this value, simplifying the comparison of a consolidated loan offer against your current obligations and helping you assess the overall cost of your financing.

The Core Concept

The blended rate is essentially the weighted average of the interest rates on two or more amortizations that share the same payment period. By combining individual balances and their respective rates into one figure, you can treat multiple debts as a single obligation for interest calculations or evaluate a new loan offer against your existing portfolio.

Formula for Blended Rate

The blended rate is computed by dividing the total interest due for a given payment period by the total outstanding principal. Mathematically:

$$\text{blended rate} = \frac{\sum_{i=1}^{n} (B_i \times r_i)}{\sum_{i=1}^{n} B_i}$$

where $B_i$ is the balance of the $i$-th amortization and $r_i$ is its periodic interest rate (both must refer to the same time period). This equation is equivalent to summing the interest amounts and dividing by the sum of balances.

Example 1: Credit Card Purchases for a Workshop

Suppose you buy equipment for your workshop from three stores, each on a separate credit line with its own monthly interest rate:

Store	Items	Balance	Monthly Interest Rate	Payment Term
A	Laser printer	$2,000	2%	6 months
B	3D printer + filaments	$3,000	4%	10 months
C	Plotter cutter	$200	3%	3 months

All payment periods are monthly, so a blended rate is meaningful. For the first month:

• Interest from Store A: \2{,}000 \times 0.02 = $40 $
• Interest from Store B: \3{,}000 \times 0.04 = $120 $
• Interest from Store C: \200 \times 0.03 = $6 $

Total balance = \5{,}200 $. Total interest =$ $166 $. Therefore:

$$\text{blended rate} = \frac{\$166}{\$5{,}200} = 0.031923 = 3.192\%$$

This means that for the first three months (until the plotter cutter is paid off), the combined balance of $5,200 effectively incurs interest at a blended monthly rate of 3.192%.

Example 2: Mortgage Top‑Up Scenario

Imagine you have an existing mortgage of $100,000 at an annual rate of 2.5$20,000 at a 4% annual rate, giving you extra cash. To evaluate this offer, calculate the blended annual rate:

$$\text{blended rate} = \frac{(\$100{,}000 \times 0.025) + (\$20{,}000 \times 0.04)}{\$100{,}000 + \$20{,}000} = \frac{\$2{,}500 + \$800}{\$120{,}000} = \frac{\$3{,}300}{\$120{,}000} = 0.0275 = 2.75\%$$

If you accept the offer, the effective interest rate on the new total balance of $120,000 becomes 2.75%. This number helps you directly compare the lender’s proposal with other financing options or simply understand your new cost of borrowing.

How to Use the Blended Rate Calculator

The tool is straightforward: enter the outstanding balance and the corresponding periodic interest rate for each loan, mortgage, or debt you wish to combine. All rates must be expressed for the same payment frequency (e.g., all monthly or all annually). You can input details for up to ten amortizations—just fill in a row, and the next blank field appears automatically. The calculator instantly displays the total combined balance and the blended rate at the bottom. Remember that mixing different payment periods invalidates the blended rate; ensure consistency before relying on the result.

Whether you are consolidating credit card debt, refinancing student loans, or evaluating a mortgage increase, the blended rate gives you a clear, single metric to guide your financial decisions.