How this calculator works
Payment = P × r ÷ (1 − (1 + r)−n), where P is the loan amount, r the monthly rate (annual rate ÷ 12) and n the number of monthly payments. At a 0% rate the payment is P ÷ n. Total interest = payment × n − P.
What each input means
| Input | What it is actually asking |
|---|---|
| Loan amount | What you borrow, not the project cost. Leave out any part you pay in cash. |
| Rate | The annual rate on your offer. A variable rate changes the payment later; this tool uses one rate. |
| Term | Years to repay. Longer terms lower the payment and raise total interest. |
| Rent | Optional. The monthly rent you expect, before vacancy and costs. |
Worked examples
Including one where the naive answer misleads, which is the example most calculators leave out.
Comparing two terms
Run the same amount and rate at two terms. The shorter term shows a higher payment and a much smaller total interest line. Choose by the payment your budget can carry, not by the total alone.
Payment against rent
Type an expected rent. If the result says the rent falls short, the ADU needs other income to carry the loan, before vacancy, repairs, insurance and tax.
What changes the result
The rate moves the payment most for long terms. A HELOC or construction loan can be interest-only for a period, which this tool does not model; compare routes in the financing comparison.
When not to use this
Do not use the result as an approval. Lenders set their own rules on income, value and whether future ADU rent counts; see our financing research.
Questions this calculator answers
- What loan types are used for ADUs?
- Cash-out refinances, HELOCs, home equity loans, construction and renovation loans. Each has its own terms; the financing pages are held for review.
- Does this include taxes and insurance?
- No. It covers principal and interest only.
- Why are there no default numbers?
- Because any default would be a guess about your loan. Type the offer you have.
- Can ADU rent help me qualify?
- Some lenders count it under specific rules; many do not count projected rent. Ask your lender.
Sources and methodology
Figures dated 27 October 2026. Last reviewed .
- Fair Market Rents, FY2026 (HUD, retrieved 2026-09-05. Suggested benchmark for the optional rent input; not shipped as a value.)
- HyreADU research: ADU financing landscape (HyreADU, retrieved 2026-09-05. Why projected rent often does not qualify a loan.)
Related
- ADU payback calculator Years until rent recovers the cost.
- Financing comparison Four routes on your quoted rates.
- ADU financing How each loan type works.