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Finance Calc Kit
Mortgages

Mortgage Penalty Calculator

Calculate early mortgage payoff penalties, comparing 3 months interest vs. interest rate differential (IRD) penalties.

Mortgage details

$
%
%
months

Estimated prepayment penalty

$11,250.00

Interest rate differential (IRD is higher)

Calculation details

3 months interest penalty$4,125.00
IRD penalty$11,250.00

How prepayment penalties are estimated

Lenders commonly use the greater of three months interest or the interest rate differential on fixed-rate loans.

  1. Three months interest penalty

    Penalty3mo=B×r×312\text{Penalty}_{3\text{mo}} = B \times r \times \frac{3}{12}

    On a $300,000.00 balance at 5.5%, three months of interest equals $4,125.00.

  2. Interest rate differential (IRD)

    PenaltyIRD=B×(r−rc)×n12\text{Penalty}_{\text{IRD}} = B \times (r - r_c) \times \frac{n}{12}

    With 36 months remaining and a comparison rate of 4.3%, the IRD estimate is $11,250.00.

  3. Select the applicable rule

    Penalty=max⁡(Penalty3mo,PenaltyIRD)\text{Penalty} = \max(\text{Penalty}_{3\text{mo}}, \text{Penalty}_{\text{IRD}})

    Fixed-rate loans use whichever method produces the higher fee. Interest rate differential (IRD is higher).

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What is a mortgage prepayment penalty?

A prepayment penalty is a fee some lenders charge when you pay off all or a large portion of your mortgage before the end of the loan term. It compensates the lender for interest income they expected to collect. Many modern residential loans have no prepayment penalty, but older or specialty loans may still include one.

This calculator estimates two common methods: three months of interest and the interest rate differential (IRD). Fixed-rate loans typically use whichever method produces the higher fee. Variable-rate loans usually apply only the three months interest rule. Before refinancing or paying off early, model your savings with the mortgage payoff calculator and compare against the penalty shown here. To size your base payment, use the EMI calculator or the mortgage calculator.

Three months interest penalty

This method charges interest equal to three months at your current contract rate on the remaining balance:

Where B is the remaining balance and r is the annual interest rate as a decimal.

Interest rate differential (IRD)

On fixed-rate loans, lenders may also calculate a penalty based on the difference between your contract rate and a current market comparison rate, multiplied by the remaining term:

Where r_c is the comparison or prevailing market rate and n is the remaining months on your term. If the comparison rate is higher than your contract rate, the differential is zero.

Worked example

On a $300,000 remaining balance at 5.5% with 36 months left, three months of interest equals $4,125. If the comparison rate is 4.25%, the rate differential is 1.25 percentage points and the IRD estimate is $11,250. On a fixed-rate loan, the lender would use the higher amount: $11,250.

Important limitations

  • Actual penalties vary by lender, loan type, and state law. Always request a payoff quote from your servicer.
  • Some loans allow partial prepayment up to a limit without penalty.
  • IRD calculations can use different comparison rates or discounting methods than this simplified estimate.

Frequently asked questions

Do all mortgages have prepayment penalties?
No. Most modern U.S. residential mortgages do not include prepayment penalties, especially FHA, VA, and USDA loans. Always check your loan documents or ask your servicer.
Why does a variable-rate loan only use three months interest?
Variable-rate loans typically reset with market rates, so lenders often apply only the three months interest method rather than an interest rate differential.
What comparison rate should I use for IRD?
Lenders set their own comparison or posted rate. Use the best available market rate for a similar term as a rough estimate, then confirm with your lender payoff statement.
Is a prepayment penalty tax deductible?
In some cases prepayment penalties may be treated as mortgage interest for tax purposes, but rules vary. Consult a tax professional for advice specific to your situation.
Should I still pay off early if there is a penalty?
Compare the penalty to your projected interest savings using the mortgage payoff calculator. If savings exceed the fee and you have no better use for the cash, early payoff may still make sense.
Are my inputs stored on a server?
No. All calculations run in your browser. Changing inputs updates the page URL so you can bookmark or share a scenario.

Resources and references

The formulas and methods in this calculator were checked against these independent sources.