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What this calculator does
Co-signing makes you responsible if the borrower defaults. This calculator shows the impact on your DTI and what a missed payment could do to your score.
The math
New DTI = (existing debt + co-signed loan) ÷ gross income. If DTI > 40%, a warning appears. A missed payment subtracts a fixed 80 points from the score.
Worked example
Adding a $20,000 loan to $500 existing debt with $50,000 income raises DTI to 41%, triggering a warning.
Why this matters
Legal and medical bills are stressful and opaque. This calculator gives you a starting number and a concrete next question to ask.
Methodology and transparency
This page publishes the exact formula used to compute the result, so you can verify it in a spreadsheet or check the assumptions against your own situation. The worked example uses the tool default inputs; change any number and the result updates live in your browser. No data is sent or stored.
Common questions
Should I ever co-sign?
Only if you are prepared to pay the full loan yourself.
Can I remove myself from a co-signed loan?
Usually only if the borrower refinances alone or the loan is paid off.