Cosigner Loan Risk Calculator
See the monthly payment you'd be liable for, your before-and-after debt-to-income ratio, and the mortgage buying power you'd give up — before you co-sign.
Your exposure if you sign
- Monthly payment you're liable for
- $400.76
- Total obligation (60 payments)
- $24,045.54
= $20,000 · r(1+r)ⁿ/((1+r)ⁿ−1), r = 7.5%/12, n = 60
Excludes late fees and collection costs — lenders can pursue you directly
Your debt-to-income ratio
- Before cosigning
- 30.00%
- Cosigned payment added
- + $400.76/mo
= ($1,800 + $400.76) ÷ $6,000
Most underwriting counts a cosigned payment as your debt — see sources
Borrowing power at a 43% DTI cap
Payment room for new credit
$780.00 → $379.24
≈ Mortgage you could support (30-yr @ 6.5%)
$123,400 → $60,000
Cosigning this loan costs you ≈ $63,400 in mortgage buying power until you're released.
Your two exits
Cosigner release: many lenders offer release after a run of on-time payments by the primary borrower (commonly 12–48 — check the loan agreement before signing; it is not automatic). Refinance: the primary borrower refinances in their own name once their credit qualifies, which closes the cosigned loan entirely.
How to use
- Enter the loan being cosigned: amount, APR, and term in months.
- Enter your own gross monthly income and current monthly debt payments.
- Adjust the DTI cap and the missed-payments slider to see your exposure, your new debt-to-income ratio, and the buying power you'd give up.
How it works
When you cosign, you are not a character reference — you are a borrower. The lender can collect the full debt from you directly, and most underwriting counts the loan's monthly payment as your own debt the moment you sign.
This calculator computes three figures from the standard amortization formula M = P·r(1+r)ⁿ/((1+r)ⁿ−1) and the CFPB's definition of debt-to-income ratio (monthly debt payments ÷ gross monthly income): the payment you're liable for, your DTI before and after signing, and how much loan a lender could still extend you at a given DTI cap — before vs. after the cosigned payment is counted against you.
All calculation happens in your browser. Your numbers never leave your device.
Frequently asked questions
Does cosigning a loan affect my debt-to-income ratio?
Yes. For most underwriting, the full monthly payment on a loan you cosigned counts as your own debt when you apply for credit — even if the primary borrower makes every payment. Fannie Mae guidelines allow lenders to exclude it only when the primary borrower can document 12 months of on-time payments from their own funds.
Does cosigning hurt my credit score?
The loan appears on your credit report as your obligation. If every payment is on time, the effect can be neutral or mildly positive; but any late payment is reported on your credit report too, exactly as if you had missed it yourself. Score models are proprietary, so this tool reports dollar amounts, not score points.
What happens if the primary borrower misses a payment?
You owe it. As a cosigner you are 100% liable for the full debt — the lender does not have to chase the primary borrower first. Use the missed-payments slider above to see the cash cost; note it excludes late fees and collection costs, which are added on top.
How do I get released from a cosigned loan?
Two paths: a cosigner release program (many lenders offer release after a documented run of on-time payments, commonly 12–48, but it is never automatic — check the loan agreement before you sign), or the primary borrower refinancing the loan in their own name once their credit qualifies.
Can I still get a mortgage after cosigning?
Yes, but the cosigned payment usually counts against your debt-to-income ratio, which shrinks the loan size you qualify for. The borrowing-power panel above shows the approximate mortgage difference at your chosen DTI cap.
How is the monthly payment calculated?
With the standard loan amortization formula: M = P·r(1+r)ⁿ/((1+r)ⁿ−1), where P is the amount borrowed, r the monthly interest rate (APR ÷ 12), and n the number of monthly payments. The worksheet above shows this formula with your numbers substituted in.
Related tools
This tool is an educational estimate, not financial or credit advice. Lender underwriting, release policies, and fees vary — read the loan agreement and consider talking to a financial professional before cosigning.