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Down Payment Calculator

Converts a down payment given as an amount or a percentage of the home price into the loan amount and loan-to-value ratio, flags whether private mortgage insurance is likely (LTV above 80 %) and estimates its annual and monthly cost at a given PMI rate.

When to use

You want to know how much you will borrow and whether PMI applies for a given home price and down payment, or how much more cash reaches 20 % down.

Do not use when: You need the monthly mortgage payment (use mortgage-payment) or a savings plan to reach the down payment (use savings-goal).

Formula

down_payment = down_payment_amount or home_price × down_payment_percent/100; loan_amount = home_price − down_payment; LTV = loan_amount / home_price × 100; PMI likely if LTV > 80; annual_pmi = loan_amount × pmi_rate_percent/100

The 80 % LTV threshold applies to conventional (Fannie Mae/Freddie Mac) loans; FHA loans charge mortgage insurance at any LTV and VA loans charge none. PMI rates vary with credit score, LTV and loan type, so the estimate is indicative only.

Inputs

Parameter	Type	Unit	Required	Description
`home_price`	number		yes	Purchase price of the home. Range: > 0, ≤ 10000000000
`down_payment_amount`	number		no	Down payment in currency; takes precedence over down_payment_percent when both are given. Range: ≥ 0, ≤ 10000000000
`down_payment_percent`	number	%	no	Down payment as a percent of home_price (used when down_payment_amount is omitted). Range: ≥ 0, ≤ 100
`pmi_rate_percent`	number	% of loan/year	default 0.75	Annual private mortgage insurance premium as a percent of the loan amount; typical range 0.3–1.5 % depending on credit score and LTV. Range: ≥ 0, ≤ 5

Outputs

Output	Type	Unit	Description
`down_payment`	number		Down payment in currency.
`down_payment_percent`	number	%	down_payment / home_price × 100.
`loan_amount`	number		home_price − down_payment.
`loan_to_value_percent`	number	%	loan_amount / home_price × 100.
`pmi_likely`	boolean		True when LTV exceeds 80 % (conventional loans usually require PMI).
`estimated_annual_pmi`	number		loan_amount × pmi_rate_percent / 100 when PMI is likely, otherwise 0.
`estimated_monthly_pmi`	number		estimated_annual_pmi / 12.
`down_payment_for_20_percent`	number		0.2 × home_price, the amount that avoids PMI on conventional loans.
`additional_needed_for_20_percent`	number		max(0, down_payment_for_20_percent − down_payment).
`assessment`	string		Plain-language note on the LTV and PMI status.

Example

350,000 home, 10 % down: {"home_price":350000,"down_payment_percent":10} → {"down_payment":35000,"down_payment_percent":10,"loan_amount":315000,"loan_to_value_percent":90,"pmi_likely":true,"estimated_annual_pmi":2362.5,"estimated_monthly_pmi":196.88,"down_payment_for_20_percent":70000,"additional_needed_for_20_percent":35000}

500,000 home, 100,000 down: {"home_price":500000,"down_payment_amount":100000} → {"down_payment":100000,"down_payment_percent":20,"loan_amount":400000,"loan_to_value_percent":80,"pmi_likely":false,"estimated_annual_pmi":0,"additional_needed_for_20_percent":0}

GET https://tttkmbb.com/api/v1/calculate/down-payment?home_price=350000&down_payment_percent=10

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/down-payment (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/down-payment · Markdown: https://tttkmbb.com/finance/down-payment.md · JSON definition: https://tttkmbb.com/finance/down-payment.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="down-payment"
OpenAPI operationId: calculate_down_payment
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

CFPB – What is private mortgage insurance? (government)
Wikipedia – Loan-to-value ratio (reference)
CFPB – Owning a Home: loan costs and monthly payment components (government)

FAQ

When does PMI stop?

Under the US Homeowners Protection Act you can request cancellation at 80 % LTV based on the original value, and the lender must cancel automatically at 78 % if payments are current.

Is exactly 20 % down enough to avoid PMI?

Yes: PMI is required when LTV is above 80 %, so a 20 % down payment (LTV = 80 %) avoids it on conventional loans.

Related calculators

Mortgage Payment Calculator — Monthly payment on the resulting loan amount.
Savings Goal Calculator — Monthly saving needed to reach the down payment.
Debt-to-Income Ratio Calculator — Check whether the payment fits lender DTI limits.