Debt-to-income, usually shortened to DTI, answers a straightforward question: how much of the monthly income in your model is already committed to housing and debt payments? The formula is simple; deciding what the number means requires more context.
The Bethemesh debt-to-income calculator separates income, housing costs and other debts. It shows a housing ratio, total DTI, income left after commitments and the mathematical room before an adjustable reference threshold.
That makes DTI useful for reviewing a budget, preparing for financing or understanding why two people with the same income can have very different borrowing capacity.
Debt-to-income ratio = Monthly commitments / Monthly income × 100
If you use $3,000 of monthly income and $900 of monthly commitments, the mathematical ratio is 30%.
The arithmetic is not the hard part. Consistency is. A useful calculation needs a clear definition of the income and obligations included. Bethemesh keeps those inputs separate so you can see the assumptions rather than hiding everything behind one “expenses” field.
Which income should you use?
For personal planning, start with the regular income you want to compare with your obligations: earned income plus other recurring income that belongs in your scenario.
This is not an attempt to reproduce every lender’s underwriting policy. Lenders may treat bonuses, variable income, rental income or recent earnings differently. If a source of income is uncertain, run one conservative scenario without it and another with it. The difference tells you how sensitive your DTI is to that assumption.
If you first need to convert hourly or annual pay to a monthly basis, use the salary calculator.
Which debts and housing costs belong in the calculation?
The calculator separates housing from other debts for a reason.
Housing can include rent or a mortgage payment plus recurring property taxes, insurance or housing fees that you choose to include. Dividing those housing costs by income produces the housing ratio.
Other debts can include required credit-card or revolving-credit payments, auto loans, student loans, personal loans and other recurring debt obligations. Add them to housing and you get the commitments used for total DTI.
This breakdown is more useful than a single percentage because it shows what is driving the result.
Housing ratio versus total DTI
Suppose monthly income is $4,000, housing costs are $1,000 and other debt payments are $400. The housing ratio is 25%. Total DTI is 35% because total commitments are $1,400.
The two ratios answer different questions. Housing ratio isolates the cost of housing; total DTI captures the broader set of obligations in the model.
The DTI calculator displays both so you do not have to collapse them into one number.
Is there one “good” DTI threshold?
No single threshold applies to every lender, product and country. A percentage can be a useful planning reference, but it should not be presented as an automatic approval or rejection rule.
That is why Bethemesh makes the reference threshold editable. You can ask, “How much monthly room would remain if I used this threshold?” without claiming that a lender will use the same rule.
Actual credit decisions can consider income stability, reserves, credit history, household circumstances, collateral, insurance, residual income and product-specific requirements.
Why residual income matters
Percentages can hide scale. Two households can both have a 30% DTI while having very different amounts of money left after commitments.
With $2,000 of income, 30% committed leaves $1,400 before other living expenses. With $6,000 of income, the same ratio leaves $4,200. The percentage is identical; the cash position is not.
The calculator therefore displays income left after commitments alongside DTI. It is not a full cost-of-living budget, but it stops the percentage from becoming the only thing you look at.
If you choose a 35% reference threshold, the calculator can derive the total commitments represented by that assumption:
Commitments at threshold = Income × 35%
It then subtracts current commitments. A positive result is the mathematical room before the selected threshold. If current commitments already exceed it, the available room is zero rather than a fictional new borrowing allowance.
This is especially useful before a mortgage affordability calculation because it helps establish a starting point for a possible new payment.
What happens when you add a new loan payment?
A new loan adds another monthly obligation. You can estimate the impact before borrowing.
For example, $3,500 of income and $700 of current commitments produces a 20% DTI. Add a $500 payment and commitments rise to $1,200, or roughly 34.3%.
Scenario testing helps answer practical questions: What if the auto loan is still active? What if it ends before the mortgage starts? How much payment can you add while preserving the buffer you want?
For a home purchase, the mortgage affordability calculator takes the next step by turning available payment capacity into an estimated loan amount using rate and term.
DTI is not the same as borrowing capacity
DTI describes the relationship between income and monthly obligations. Borrowing capacity estimates how much principal a new payment might finance.
To move from one to the other, you need more information: interest rate, loan term and, for a home-buying budget, the down payment.
The tools therefore form a sequence rather than duplicates: use DTI to understand the monthly budget, mortgage affordability to estimate a possible home-loan amount, and the loan calculator to analyze a specific principal and its amortization.
Three common mistakes
First, do not mix periods. Annual income cannot be compared directly with monthly debt payments; convert everything to a consistent basis.
Second, do not ignore a debt simply because it will end soon. Include it in the current scenario, then create a second scenario after payoff to see the difference.
Third, do not confuse “below my threshold” with “comfortable.” Look at the dollars left after commitments and compare them with your real living expenses and savings goals.
A practical way to use DTI
Start by entering your current situation only. Check housing ratio, total commitments, DTI and remaining income. Then change one assumption at a time: remove a debt that will soon be repaid, test a proposed payment, or adjust the reference threshold.
Finally, keep a conservative case. Financial calculators are most useful when they reveal sensitivity and margin, not when they are used only to produce the largest possible number.
Key takeaway
DTI is simple, but it becomes useful only when the inputs are transparent. Know which income you included, separate housing from other debt, and read residual income alongside the percentage.
Start with the debt-to-income calculator, continue with the guide to mortgage affordability, and use the loan calculator when you are ready to analyze a specific financing scenario.
