Effective Interest Rate
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When applying for a personal loan, mortgage, or credit card, lenders advertise a “Stated Interest Rate” or Annual Percentage Rate (APR). However, if your debt compounds monthly or daily—or if the lender charges upfront origination fees—the true cost of your loan is significantly higher than the advertised rate. To find your true borrowing cost, you must calculate the Effective Interest Rate (EIR), also known as the Effective Annual Rate (EAR).
Our free Effective Interest Rate Calculator reveals the true cost of credit. By inputting your nominal APR, compounding frequency, and loan fees, you can make informed borrowing decisions and avoid predatory lending traps.
How to Calculate Effective Interest Rate (EAR)
The basic Effective Interest Rate formula accounts for intra-year interest compounding.
The EAR Compounding Formula:
EAR = (1 + r / n)ⁿ - 1
- r: Stated nominal annual rate (APR) as a decimal.
- n: Number of compounding periods per year (Monthly = 12, Daily = 365).
Effective Rate Including Upfront Loan Fees
When a lender charges upfront origination points or administrative processing fees, your actual net loan proceeds decrease while your interest payments stay the same, driving your true EIR even higher:
True EIR with Fees = Total Annual Interest & Fee Charges / Net Cash Proceeds Received
Credit Card Rates: Stated APR vs. True Effective Rate
Credit cards compound interest on a daily basis. Here is how daily compounding increases borrowing costs across popular credit card APRs:
| Credit Card Stated APR | Compounding Frequency | True Effective Annual Rate (EAR) | Annual Extra Cost per $10,000 Balance |
|---|---|---|---|
| 12.00% | Daily (365x/yr) | 12.747% | +$74.70 |
| 18.00% | Daily (365x/yr) | 19.716% | +$171.60 |
| 24.00% | Daily (365x/yr) | 27.115% | +$311.50 |
| 29.99% (Store Card) | Daily (365x/yr) | 34.954% | +$495.40 |
Step-by-Step Loan Fee Example
Imagine taking out a $10,000 personal loan with a stated APR of 10.00% compounded monthly, plus a 3% ($300) upfront origination fee deducted from your payout.
Step 1: Calculate EAR from Compounding
EAR = (1 + 0.10 / 12)¹² - 1 = (1.00833)¹² - 1 = 10.47%
Step 2: Account for Upfront Fee
Because the lender takes $300 upfront, you only receive $9,700 in net cash, but you pay interest on the full $10,000.
Your true effective borrowing rate increases to 13.88% for Year 1!
Frequently Asked Questions (FAQ)
What is the difference between APR and Effective Interest Rate?
APR (Annual Percentage Rate) is the simple, non-compounded annual rate mandated by US Truth in Lending disclosures. Effective Interest Rate (EIR/EAR) incorporates the financial impact of daily/monthly compounding, reflecting what you actually pay.
Why is Effective Rate important when comparing loans?
Comparing a loan with 8.00% daily compounding to a loan with 8.20% annual compounding can be deceiving. Converting both to Effective Interest Rate reveals that the 8.20% annual loan is actually cheaper than the 8.00% daily loan!
Does Truth in Lending (TILA) require EAR disclosure?
In the United States, TILA requires lenders to disclose APR and total finance charges. However, because credit card companies compound interest daily, consumer advocates recommend calculating EAR to understand the real cost of carrying a monthly card balance.