Applying for a mortgage with a partner or family member? Use our Cosigner Mortgage Calculator to estimate your monthly payments and check your combined Debt-to-Income (DTI) ratio to see if adding a cosigner helps you qualify.
Cosigner Mortgage Calculator
Enter monthly incomes to calculate combined DTI.
Cosigner Mortgage Calculator Formula
This tool uses two formulas: one for the monthly mortgage payment (Principal & Interest) and one for the Debt-to-Income (DTI) ratio, which determines qualification with a cosigner.
DTI Ratio = (Total Housing Payment + Other Monthly Debts) / (Borrower Income + Cosigner Income)
Formula Source: CFPB DTI Guidelines
Variables
- P = Principal Loan Amount (Home Price – Down Payment).
- i = Monthly Interest Rate (Annual Rate / 12).
- n = Total Months (Years x 12).
- Cosigner Income = The gross monthly income of the non-occupant cosigner.
- Total Debts = The sum of minimum monthly payments for both the borrower and cosigner (credit cards, student loans, etc.).
Related Calculators
- Debt-to-Income (DTI) Calculator
- FHA Loan Calculator
- Mortgage Affordability Calculator
- Rent vs. Buy Calculator
What is a Cosigner Mortgage Calculator?
A Cosigner Mortgage Calculator is a specialized tool designed to help homebuyers determine if adding a cosigner (such as a parent or relative) will improve their mortgage approval chances.
When you add a cosigner, their income is added to yours, which lowers the overall Debt-to-Income (DTI) ratio. This is often critical for borrowers who have good credit but insufficient income to qualify for the loan amount they need. This calculator provides both the estimated monthly payment and the new “Blended DTI” to show the impact of the cosigner’s financial strength.
How to Calculate Cosigner Mortgage Eligibility (Example)
- Loan Payment: For a $320,000 loan at 7%, the Principal & Interest is ~$2,129/mo. Assuming taxes/insurance add $500, total housing cost is $2,629.
- Borrower Situation: The borrower earns $5,000/mo. DTI = $2,629 / $5,000 = 52.6%. This is typically too high for approval.
- Add Cosigner: A parent joins as cosigner earning $4,000/mo.
- Combined Income: Total income is now $9,000/mo.
- New DTI Calculation: $2,629 / $9,000 = 29.2%. This is well within the safe approval range (usually under 43%).
Frequently Asked Questions (FAQ)
1. Does a cosigner’s debt count against me?
Yes. While their income helps, their monthly debts (car loans, their own mortgage) are also added to the calculation. This calculator allows you to input “Total Monthly Debts” to see the net effect.
2. How much income does a cosigner need?
There is no fixed amount, but they must earn enough to cover their own debts plus your new mortgage payment while maintaining a healthy DTI ratio.
3. Does being a cosigner affect credit score?
Yes. The mortgage appears on the cosigner’s credit report. Late payments will damage both the borrower’s and the cosigner’s credit scores.
4. Can I remove a cosigner later?
Generally, yes, but you usually have to refinance the mortgage into your own name once your income has increased enough to qualify on your own.