Calculators / Developers
Calculator API
Every calculator on this site can be run from your own code or website. The API is free, needs no key, and returns JSON. If you just want a calculator on your page, the widget is easier.
An OpenAPI 3.1 description of the API is at /openapi.json. You can load it into Postman, Swagger UI or a client generator. To try every calculator without writing code, open the Postman workspace; each request is filled in with example inputs.
Endpoints
GET /api/v1/calculators
Lists all calculators.
GET /api/v1/calculators/{slug}
Describes one calculator: each input's key, label, kind (money, percent, years, months, number, select, toggle, month), default value, limits and choices. A month input takes a calendar month such as 2026-11. Optional inputs have a placeholder that says what is used when you leave them out.
GET /api/v1/calculators/{slug}/calculate?Key=value&…
Runs the calculator. Any input you leave out uses its default. Values may include $, , and %. Add include=schedule to get a year-by-year amortization schedule.
POST /api/v1/calculators/{slug}/calculate
The same, with the inputs as a JSON object in the body.
Example
curl "https://mortgagecalculator.me/api/v1/calculators/mortgage-payment-calculator/calculate?HomeValue=375000&DownPayment=20&Rate=6.5&Term=30"
{
"calculator": "mortgage-payment-calculator",
"headline": "",
"errors": [],
"values": { "PrincipalAndInterest": 1896.20, "TotalMonthlyPayment": 2427.45, "TotalInterest": 382636.71, … },
"sections": [ { "title": "…", "columns": [ … ], "rows": [ { "label": "…", "values": [ "…" ] } ] } ],
"charts": [ … ],
"notes": [ … ],
"url": "https://mortgagecalculator.me/Mortgage-Calculator/mortgage-payment-calculator?HomeValue=375000&DownPayment=20&Rate=6.5&Term=30"
}
headline gives a one-sentence answer for calculators that have one. sections holds the same tables shown on the calculator page, already formatted. values holds the key numbers unformatted. url opens the full results on this site.
Errors and limits
- Invalid inputs return status 400 with a list of messages in
errors.
- An unknown calculator returns 404.
- Each visitor IP can make 120 requests a minute. Past that the API returns 429; wait a minute and try again.
- The API can be called from any website (CORS is open). It never stores what you send.
Calculators and their inputs
Mortgage Payment Calculator mortgage-payment-calculator
| Key | Input | Default |
|---|
HomeValue |
Home price |
375000 |
DownPayment |
Down payment |
20 |
DownPaymentUnit |
Units for DownPayment (pct, usd) |
pct |
Balance |
Loan amount |
|
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
LoanType |
Type of loan |
Conventional |
StartDate |
First payment |
|
AnnualPropertyTaxes |
Property taxes |
1.2 |
AnnualPropertyTaxesUnit |
Units for AnnualPropertyTaxes (pct, usd) |
pct |
AnnualInsurance |
Homeowners insurance |
0.5 |
AnnualInsuranceUnit |
Units for AnnualInsurance (pct, usd) |
pct |
AnnualPMI |
Private mortgage insurance (PMI) |
0.5 |
AnnualPMIUnit |
Units for AnnualPMI (pct, usd) |
pct |
MonthlyHOA |
HOA dues per month |
0 |
Mortgage Refinance Calculator mortgage-refinance-calculator
| Key | Input | Default |
|---|
Balance |
Original loan amount |
300000 |
Rate |
Current interest rate |
7.5 |
Term |
Loan term |
30 |
MonthsPayed |
Payments made so far |
36 |
NewRate |
New interest rate |
6.25 |
NewTerm |
New loan term |
30 |
Points |
Points |
0 |
OriginationFees |
Origination fee |
1 |
OriginationFeesUnit |
Units for OriginationFees (pct, usd) |
pct |
ClosingCosts |
Other closing costs |
3000 |
YearsBeforeSell |
Years until you sell or refinance again |
7 |
Additional Payment Calculator additional-payment-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
StartDate |
First payment |
|
AdditionalPayment |
Extra each month |
200 |
MonthlyExtraStart |
Monthly extra starts |
|
MonthlyExtraEnd |
Monthly extra stops after |
|
QuarterlyExtra |
Extra every 3 months |
0 |
QuarterlyExtraStart |
Quarterly extra starts |
|
YearlyExtra |
Extra once a year |
0 |
YearlyExtraStart |
Yearly extra starts |
|
OneTimeExtra |
One-time extra payment |
0 |
OneTimeExtraDate |
One-time payment month |
|
APR Calculator apr-calculator
| Key | Input | Default |
|---|
LoanType |
Type of loan |
Conventional |
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
InterestRateFixedRateTerm |
Interest-only period (years) |
0 |
CurrentHouseValue |
Home value |
375000 |
Points |
Discount points |
1 |
OriginationFees |
Origination fee |
1000 |
BrokerFee |
Mortgage broker fee |
0 |
TaxFloodService |
Tax and flood service fees |
100 |
AssumptionFee |
Underwriting / processing fees |
500 |
RequiredCreditLife |
Required credit life or disability insurance |
0 |
LockCommitmentFee |
Rate lock / commitment fee |
0 |
OtherAPRFees |
Other finance charges |
0 |
UMIP |
Upfront mortgage insurance premium |
0 |
MMIP |
Annual mortgage insurance premium |
0 |
Which Loan Is Better Calculator which-loan-is-better-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
YearsToKeep |
Years you expect to keep the loan |
10 |
OriginationFeesUnit |
Enter origination fees as |
usd |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
Points |
Points |
0 |
OriginationFees |
Origination fee |
1000 |
ClosingCosts |
Other closing costs |
3000 |
Rate2 |
Interest rate |
6.0 |
Term2 |
Loan term |
30 |
Points2 |
Points |
1.5 |
OriginationFees2 |
Origination fee |
1000 |
ClosingCosts2 |
Other closing costs |
3000 |
Mortgage Points Calculator mortgage-points-calculator
| Key | Input | Default |
|---|
LoanType |
Purpose of loan |
Purchase |
Balance |
Loan amount |
300000 |
Term |
Loan term |
30 |
YearsBeforeSell |
Years you expect to keep the loan |
7 |
LowInterest |
Interest rate |
6.0 |
HighPoints |
Points |
2 |
HighInterest |
Interest rate |
6.5 |
LowPoints |
Points |
0 |
SavingRate |
What your savings earn |
4 |
FederalTaxRate |
Federal tax bracket |
22 |
StateTaxRate |
State tax rate |
5 |
Itemize |
I itemize deductions |
false |
Rent vs. Buy Calculator rent-vs-buy-calculator
| Key | Input | Default |
|---|
MonthlyRent |
Monthly rent |
2200 |
AnnualRentIncrease |
Rent increase per year |
3 |
HomeValue |
Home price |
375000 |
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
Points |
Points |
0 |
ClosingCosts |
Other closing costs |
6000 |
AnnualPropertyTaxes |
Property taxes |
1.2 |
AnnualPropertyTaxesUnit |
Units for AnnualPropertyTaxes (pct, usd) |
pct |
AnnualInsurance |
Homeowners insurance |
0.5 |
AnnualInsuranceUnit |
Units for AnnualInsurance (pct, usd) |
pct |
AnnualPMI |
PMI |
0.5 |
AnnualPMIUnit |
Units for AnnualPMI (pct, usd) |
pct |
AnnualMaintenance |
Maintenance and repairs per year |
3750 |
AnnualAppreciation |
Home price growth per year |
3 |
YearsBeforeSell |
Years before you sell |
7 |
SellingCost |
Selling costs |
6 |
InvestmentReturn |
What your savings earn |
0 |
FederalTaxRate |
Federal tax bracket |
22 |
StateTaxRate |
State tax rate |
5 |
Deductions |
Other itemized deductions per year |
10000 |
StandardDeduction |
Standard deduction |
32200 |
How Much Income Do I Need to Qualify? how-much-income-do-i-need-to-qualify
| Key | Input | Default |
|---|
Balance |
Home price |
375000 |
DownPayment |
Down payment |
20 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
Points |
Points |
0 |
ClosingCosts |
Other closing costs |
2 |
AnnualPropertyTaxes |
Property taxes |
1.2 |
AnnualInsurance |
Homeowners insurance per year |
1800 |
MPMI |
Monthly mortgage insurance |
0 |
MaximumRatioMonthly |
Maximum housing payment, as % of income |
28 |
MaximumRatioTotal |
Maximum total debt payments, as % of income |
36 |
Standard vs. Bi-Weekly Payment Calculator standard-vs-biweekly-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
InterestCompounded |
Interest charged |
BiWeekly |
FederalTaxRate |
Federal tax bracket |
22 |
StateTaxRate |
State tax rate |
0 |
Itemize |
I itemize deductions |
false |
Interest Only Calculator interest-only-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
Term |
Loan term |
30 |
Rate |
Conventional loan rate |
6.5 |
InterestOnlyRate |
Interest-only loan rate |
6.75 |
InterestRateFixedRateTerm |
Interest-only period (years) |
10 |
Interest Only With Additional Payment Calculator interest-only-with-additional-payment-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Interest-only term |
30 |
Amount1 |
Amount |
250 |
ExtraPaymentInterval1 |
How often |
Monthly |
StartingMonth1 |
Starting with payment # |
1 |
EndingMonth1 |
Ending with payment # (blank = end of loan) |
|
Amount2 |
Amount |
0 |
ExtraPaymentInterval2 |
How often |
Monthly |
StartingMonth2 |
Starting with payment # |
1 |
EndingMonth2 |
Ending with payment # (blank = end of loan) |
|
Amount3 |
Amount |
0 |
ExtraPaymentInterval3 |
How often |
Monthly |
StartingMonth3 |
Starting with payment # |
1 |
EndingMonth3 |
Ending with payment # (blank = end of loan) |
|
Amount4 |
Amount |
0 |
ExtraPaymentInterval4 |
How often |
Monthly |
StartingMonth4 |
Starting with payment # |
1 |
EndingMonth4 |
Ending with payment # (blank = end of loan) |
|
Amount5 |
Amount |
0 |
ExtraPaymentInterval5 |
How often |
Monthly |
StartingMonth5 |
Starting with payment # |
1 |
EndingMonth5 |
Ending with payment # (blank = end of loan) |
|
Mortgage Length Calculator mortgage-length-calculator
| Key | Input | Default |
|---|
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Original loan term |
30 |
MonthlyPayment |
Monthly payment you want to make |
2200 |
Mortgage Principal Calculator mortgage-principal-calculator
| Key | Input | Default |
|---|
Balance |
Original loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
MonthsPayed |
Payments made so far |
60 |
Mortgage Tax Benefits Calculator tax-benefits-calculator
| Key | Input | Default |
|---|
HomeValue |
Home value |
375000 |
Balance |
Loan amount |
300000 |
Rate |
Interest rate |
6.5 |
Term |
Loan term |
30 |
Points |
Points paid |
1 |
YearsBeforeSell |
Years to show |
5 |
AnnualPropertyTaxes |
Property taxes |
1.2 |
AnnualPropertyTaxesUnit |
Units for AnnualPropertyTaxes (pct, usd) |
pct |
AnnualInsurance |
Homeowners insurance |
0.5 |
AnnualInsuranceUnit |
Units for AnnualInsurance (pct, usd) |
pct |
AnnualPMI |
PMI |
0 |
AnnualPMIUnit |
Units for AnnualPMI (pct, usd) |
pct |
FederalTaxRate |
Federal tax bracket |
22 |
StateTaxRate |
State tax rate |
5 |
Deductions |
Other itemized deductions per year |
10000 |
StandardDeduction |
Standard deduction |
32200 |
Cash-Out Refinance Calculator cash-out-refinance-calculator
| Key | Input | Default |
|---|
TakeOutCash |
Cash you want to take out |
50000 |
CurrentHouseValue |
Current home value |
450000 |
YearsBeforeSell |
Years you expect to stay |
7 |
SavingRate |
What your savings earn |
4 |
FederalTaxRate |
Federal tax bracket |
22 |
StateTaxRate |
State tax rate |
5 |
Itemize |
I itemize deductions |
false |
CashForHome |
The cash will be used to improve the home |
false |
Balance |
Balance owed |
250000 |
Rate |
Interest rate |
4.0 |
Term |
Months left to pay |
300 |
MPMI |
Monthly mortgage insurance |
0 |
FirstRate |
Interest rate |
6.5 |
FirstTerm |
Term in months |
360 |
FirstPoint |
Points |
0 |
FirstClosingCost |
Closing costs |
5000 |
LoansMMIP |
Monthly mortgage insurance |
0 |
SecondRate |
Interest rate |
8.5 |
SecondTerm |
Term in months |
180 |
SecondPoint |
Points |
0 |
SecondClosingCost |
Closing costs |
1000 |
Should I Use a HELOC to Pay Off Debt? should-i-use-heloc
| Key | Input | Default |
|---|
Rate |
HELOC interest rate |
8.25 |
Term |
Years to repay the HELOC |
10 |
ClosingCosts |
HELOC closing costs |
500 |
FinanceClosingCosts |
Add closing costs to the HELOC balance |
true |
AutoLoanAmount |
Balance |
18000 |
AutoLoanInterestRate |
Interest rate |
7.5 |
AutoLoanPayment |
Monthly payment |
450 |
BoatAmount |
Balance |
0 |
BoatInterestRate |
Interest rate |
0 |
BoatPayment |
Monthly payment |
0 |
CreditCard1Amount |
Balance |
8000 |
CreditCard1InterestRate |
Interest rate |
22.9 |
CreditCard1Payment |
Monthly payment |
250 |
CreditCard2Amount |
Balance |
4000 |
CreditCard2InterestRate |
Interest rate |
19.9 |
CreditCard2Payment |
Monthly payment |
120 |
OtherAmount |
Balance |
0 |
OtherInterestRate |
Interest rate |
0 |
OtherPayment |
Monthly payment |
0 |
