Mortgage Penalty Calculator: Early Repayment Charge Estimator
Breaking your mortgage before the term ends triggers a prepayment penalty. This calculator computes both the Interest Rate Differential (IRD) and the three-months interest charge, then shows you which one your lender will collect and why. Enter your mortgage balance, rates, and term details to get an instant, itemised estimate.
How mortgage penalties are calculated
When you break a closed mortgage before the term ends, your lender charges a prepayment penalty. For variable-rate closed mortgages, this is almost always three months of interest on the outstanding balance: balance x (annual rate / 4). For fixed-rate closed mortgages, lenders compare two figures and collect whichever is larger. The first is the same three-months interest charge. The second is the Interest Rate Differential (IRD): balance x (your rate minus the lender's current posted rate for the closest matching remaining term) / 12 x months remaining. Because today's posted rates shift over time, the IRD can swing from near zero to tens of thousands of dollars depending on how far your rate sits above the current market.
What affects how large your penalty is
Four factors drive the size of the penalty. First, your outstanding balance: a larger balance scales both calculations proportionally. Second, your contracted rate relative to current posted rates: the bigger the gap, the larger the IRD. Third, how many months remain: IRD climbs linearly with months left, so the earlier you break, the costlier it is. Fourth, whether your mortgage is fixed or variable: variable-rate borrowers almost always pay less because they are limited to three-months interest. Some lenders also reduce the penalised balance by any annual prepayment privileges you have not yet used in the current calendar year, which can meaningfully lower the charge.
When breaking early might still make sense
A penalty is not automatically a reason to stay put. If refinancing to a significantly lower rate means you save more in interest over the remaining and new terms combined than the penalty costs today, breaking early can be financially rational. The key comparison is: total interest saved at the new rate over the full horizon versus penalty paid upfront plus any legal and appraisal fees (typically $500 to $2,000). A mortgage broker or bank advisor can pull your lender's exact posted rates and run an official calculation, which may differ slightly from this estimate.
Fixed vs variable: which penalty is lower
Variable-rate borrowers almost always face a lower penalty than fixed-rate borrowers breaking at the same point in a rising-rate environment. When rates rise after you lock in, the IRD becomes small or zero (since posted rates now exceed or equal your old rate), and fixed borrowers also pay only three months interest. However, in a falling-rate environment, fixed-rate borrowers face large IRD charges because their locked-in rate sits well above the lender's current posted rate. This asymmetry is one reason financial advisors often recommend fixed rates only when you are certain you will not need to break early.
Typical prepayment penalty ranges
| Scenario | Typical method | Approximate range | Severity |
|---|---|---|---|
| Variable rate, any term | 3 months interest | $500 - $4,000 | Low-moderate |
| Fixed rate, low rate diff, short term | 3 months interest | $1,000 - $5,000 | Low-moderate |
| Fixed rate, moderate rate diff, 2-3 yr left | IRD | $5,000 - $15,000 | Moderate-high |
| Fixed rate, large rate diff, 3-5 yr left | IRD | $15,000 - $40,000+ | High |
| Large balance, fixed, 5 yr left, big rate diff | IRD | $40,000+ | Very high |
Approximate penalty levels based on mortgage balance and rate differential. Actual charges vary by lender and terms.
Frequently asked questions
What is a mortgage prepayment penalty?
A mortgage prepayment penalty (also called a break penalty or early repayment charge) is a fee your lender charges when you pay off or refinance a closed mortgage before the term maturity date. Lenders include this clause to recoup the interest income they expected to earn over the full term. The charge compensates for the revenue lost when you pay ahead of schedule.
What is the Interest Rate Differential (IRD)?
The IRD is a penalty calculation used for fixed-rate mortgages. It equals your outstanding balance multiplied by the difference between your contracted rate and the lender's current posted rate for a term matching your remaining months, divided by 12, and multiplied by the number of months remaining. If your rate is 5.5% and the matching posted rate is now 4.2%, the differential is 1.3%, and you pay that gap times the balance for every remaining month. When posted rates have risen since you locked in, the IRD shrinks or disappears; when they have fallen, the IRD can be very large.
How are three months interest and IRD compared?
Your lender calculates both and charges whichever is higher. Three months interest is fixed at balance times your annual rate divided by four. The IRD rises as the rate gap widens and as more months remain. Early in a term with a significant rate differential, IRD almost always exceeds three months interest. Closer to maturity, or when rates have risen above your locked-in rate, three months interest often wins, and the IRD may even be zero.
Can I reduce the penalty using prepayment privileges?
Most closed mortgages include an annual prepayment privilege, typically 10%, 15%, or 20% of the original principal, that you can repay without penalty each year. If you have not used your full allowance in the current calendar year, many lenders will subtract the unused portion from the balance before calculating the penalty. For example, if your balance is $300,000, your privilege is 15% ($45,000), and you have not prepaid anything this year, your penalised balance could be as low as $255,000. Always confirm this with your lender before breaking.
Does this calculator give the exact penalty my lender will charge?
No. This tool provides a close estimate using the standard industry formulas, but lenders differ in which posted rate they use, whether they adjust for accrued interest, and how they handle partial months. Some lenders also add administration, discharge, or registration fees on top of the base penalty. Contact your lender directly for an official prepayment quote, which is typically provided free of charge.
Are open mortgages subject to prepayment penalties?
No. Open mortgages allow you to repay any amount at any time without penalty, which is why they carry a higher interest rate than comparable closed mortgages. This calculator covers closed mortgages only. If you have an open mortgage and want to switch lenders or pay it off early, there is no prepayment charge.
What other costs should I factor in when breaking a mortgage?
Beyond the prepayment penalty itself, expect discharge or release fees from your current lender (commonly $200 to $350), registration and legal fees for any new mortgage (typically $500 to $1,500), and potentially an appraisal fee ($300 to $600). If you are refinancing rather than selling, some lenders also require title insurance. Add these figures to the penalty to get your true cost of breaking the mortgage.