Know your monthly payment, rate, and term but not the loan amount? Work backward to find the exact principal that produces that payment.
Enter your loan details
$
%
years
Your results
$0
Loan Principal
$0
Total Interest
$0
Total Repaid
Remaining balance
How the Loan Principal Calculator works
Every fixed loan payment is the result of three numbers: the principal borrowed, the interest
rate, and the term. Usually you know the principal and solve for the payment. This calculator
does the reverse — it starts from a monthly payment, rate, and term you already know, and solves
for the principal that must have produced it.
This is useful when you know what you can pay each month, or you're trying to reconstruct the
original loan amount behind an old statement, a lender's advertised payment, or a hypothetical
scenario you're comparing against other offers.
Principal = Payment × (1 − (1 + r)^−n) / r
Here, r is your monthly interest rate (annual rate ÷ 12) and n
is the total number of monthly payments. Once the principal is found, this tool also runs it
through the full amortization schedule so you can see the resulting total interest and total
amount repaid.
Frequently asked questions
Principal is just the amount borrowed. The total cost of a loan is the principal plus all the interest you'll pay over the full term, which is always a larger number for any loan that charges interest.
The principal a given payment can support depends on both the interest rate and the term. A lower rate or a longer term lets the same monthly payment support a larger principal, because less of each payment is consumed by interest.
They use the same underlying math. The Loan Affordability Calculator is framed around budgeting — how much loan fits a payment you can afford. This tool is for finding the exact principal behind a specific payment, rate, and term you already know, such as reverse-engineering an old loan or a lender's quote.