Interest-Only Loan Calculator

Interest-Only Loan is evaluated from Loan Amount, Annual Interest Rate and Interest-Only Period. The calculation reports Interest-Only Monthly Payment, Standard P&I Payment and Payment After IO Period Ends.

Results

Thanks — we’ve logged this for review.

About the Interest-Only Loan Calculator

Interest-Only Loan is treated here as a quantitative relation between Loan Amount, Annual Interest Rate, Interest-Only Period and Total Loan Term and Interest-Only Monthly Payment, Standard P&I Payment, Payment After IO Period Ends and Interest Paid During IO Period.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
Interest-Only Payment = Loan Amount x (Annual Rate / 1200)
Standard P&I Payment = Loan x r x (1+r)^n / [(1+r)^n - 1]
Where n = total term months
Post-IO Payment = Loan x r x (1+r)^m / [(1+r)^m - 1]
Where m = remaining months after IO period
Interest During IO Period = IO Payment x IO Months

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

Interest-Only Payment = Loan Amount x (Annual Rate / 1200)
Standard P&I Payment = Loan x r x (1+r)^n / [(1+r)^n - 1]
Where n = total term months
Post-IO Payment = Loan x r x (1+r)^m / [(1+r)^m - 1]
Where m = remaining months after IO period
Interest During IO Period = IO Payment x IO Months

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: 10/20 Interest-Only Mortgage

Inputs

loan_amount: 600000 annual_rate: 7.25 io_years: 10 total_term_years: 30
Interest-Only Monthly Payment: $3,625. Standard P&I Payment: $4,093.06. Payment After IO Period Ends: $4,742.26. Interest Paid During IO Period: $435,000

With Loan Amount = 600,000, Annual Interest Rate = 7.25, Interest-Only Period = 10 and Total Loan Term = 30 as the stated inputs, the result is Interest-Only Monthly Payment = $3,625, Standard P&I Payment = $4,093.06 and Payment After IO Period Ends = $4,742.26. Each value corresponds to the declared output fields.

Example 2: 5-Year IO ARM

Inputs

loan_amount: 350000 annual_rate: 6.75 io_years: 5 total_term_years: 30
Interest-Only Monthly Payment: $1,968.75. Standard P&I Payment: $2,270.09. Payment After IO Period Ends: $2,418.19. Interest Paid During IO Period: $118,125

With Loan Amount = 350,000, Annual Interest Rate = 6.75, Interest-Only Period = 5 and Total Loan Term = 30 as the stated inputs, the result is Interest-Only Monthly Payment = $1,968.75, Standard P&I Payment = $2,270.09 and Payment After IO Period Ends = $2,418.19. Each value corresponds to the declared output fields.

Example 3: Short IO — Construction Loan

Inputs

loan_amount: 500000 annual_rate: 8.5 io_years: 1 total_term_years: 30
Interest-Only Monthly Payment: $3,541.67. Standard P&I Payment: $3,844.57. Payment After IO Period Ends: $3,873.85. Interest Paid During IO Period: $42,500

With Loan Amount = 500,000, Annual Interest Rate = 8.5, Interest-Only Period = 1 and Total Loan Term = 30 as the stated inputs, the result is Interest-Only Monthly Payment = $3,541.67, Standard P&I Payment = $3,844.57 and Payment After IO Period Ends = $3,873.85. Each value corresponds to the declared output fields.

Example 4: IO vs Full Amortization — True Cost Difference

Inputs

loan_amount: 450000 annual_rate: 7 io_years: 10 total_term_years: 30
Interest-Only Monthly Payment: $2,625. Standard P&I Payment: $2,993.86. Payment After IO Period Ends: $3,488.85. Interest Paid During IO Period: $315,000

With Loan Amount = 450,000, Annual Interest Rate = 7, Interest-Only Period = 10 and Total Loan Term = 30 as the stated inputs, the result is Interest-Only Monthly Payment = $2,625, Standard P&I Payment = $2,993.86 and Payment After IO Period Ends = $3,488.85. Each value corresponds to the declared output fields.

Common Use Cases

  • Calculate interest-only period payments on an ARM or IO mortgage
  • Compare interest-only vs fully amortizing monthly costs
  • Understand the payment shock when the IO period ends