Co-Signing Ruin Simulator
Co-Signing Risk Calculator
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, with a worked example
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. Adding a $20,000 loan to $500 existing debt with $50,000 income raises DTI to 41%, triggering a warning.
Why this matters
Co-signing is not vouching, it's borrowing: the full loan lands on your debt-to-income ratio the day you sign, and every payment the primary borrower misses hits your credit as if it were yours. The favor costs nothing only if everything goes right for years.
Methodology and transparency
New DTI = (your existing debt payments + the co-signed loan) ÷ gross income, warning above 40%; the missed-payment scenario subtracts a fixed 80 points from a credit score. Both numbers are illustrative heuristics — lenders vary their DTI ceilings, and the real score damage depends on your starting score and history (higher scores fall further). The direction is reliable; the exact magnitudes are yours to discover only the hard way. Everything runs in your browser; no data is sent or stored.
Last reviewed: 2026-08-08
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.