How the principal is worked out
The principal is the present value of your payments at the note rate divided by 12: payment × (1 − (1 + r)^−n) ÷ r. It's the reverse of the standard loan payment formula.
Worked example
$400 a month for 5 years at 11% covers a principal of $18,397.21. You pay $24,000 in total, so $5,602.79 is interest. With a $3,000 down payment, you could buy something costing $21,397.21.
Finding your original principal
Enter the payment, note rate and original term from your loan documents. The result is the amount financed through the payments.
What this calculator assumes
A fixed note rate and equal monthly payments. Lenders also apply debt-to-income limits and credit checks.
Will you qualify?
A payment you'd like isn't always one a lender will approve.
To see what a DTI limit allows, use the US loan qualification calculator .
Borrowing in the UK?
The country choices above the inputs open separate local pages. UK lenders quote an APR that already includes compounding. Choosing United Kingdom opens that page and resets the inputs; amounts are not converted.
For a UK loan, use the UK loan amount calculator in pounds.
Inputs for the US loan principal calculator
Monthly payment
The repayment you can afford, or the one on your loan, in US dollars.
Interest rate
The yearly note rate you expect, or the one in your note.
Term
How long you'll make the payments, in years.
Down payment (optional)
Money you'd put down towards a purchase. Enter 0 if none.
CALCULATOR QUESTIONS
US loan principal calculator questions
How do I calculate the principal from a payment?
Use payment × (1 − (1 + r)^−n) ÷ r, where r is the note rate ÷ 12 and n the number of payments.
How much can I borrow for $400 a month?
About $18,397 over 5 years at 11%. A longer term or lower rate raises it.
Is principal the same as the amount financed?
Not always. If fees are deducted, the amount financed is the principal minus those fees.
Does a down payment lower my payment?
It lowers the amount you need to borrow for the same purchase, so yes.