How Reverse Mortgage Interest CompoundsWith Real Examples and Calculations

Understand exactly how compound interest works on reverse mortgages. See real calculations, long-term projections, and the impact on your equity over time.

Interest Growth
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Understanding Compound Interest on Reverse Mortgages

What is Compound Interest?

Compound interest is "interest on interest." With reverse mortgages, you don't make monthly payments, so interest is added to your loan balance each year. The next year, you pay interest on both the original loan AND the previous year's interest.

Simple Example:

Year 1: $100,000 loan @ 7% = $7,000 interest

New balance: $107,000

Year 2: $107,000 @ 7% = $7,490 interest

New balance: $114,490

Year 3: $114,490 @ 7% = $8,014 interest

Notice how the interest amount increases each year, even though the interest rate stays the same. This accelerating growth is the power (and risk) of compound interest.

How It Works on Reverse Mortgages

Interest Rates in NZ

  • • Typical rates: 6.5% - 8.5% per annum
  • • Usually higher than standard mortgages
  • • Rates can be fixed or variable
  • • Some products offer rate caps

Timing

  • • Interest calculated daily
  • • Compounded annually (added to balance)
  • • No monthly payments required
  • • Debt grows every year until repaid

Key Factors

  • • Higher rates = faster debt growth
  • • Longer time = much larger debt
  • • Larger initial loan = bigger compound effect
  • • No payments = maximum compounding

Interactive Compound Interest Calculator

Choose a Scenario to Explore:

Results for: Conservative Growth Scenario

$200,000
Initial Loan
$591,775
Final Debt
$391,775
Total Interest
$654,599
Remaining Equity*

*Assumes initial house value of $800,000 growing at 3% annually

Year-by-Year Breakdown: Conservative Growth Scenario

YearLoan BalanceInterest AddedTotal InterestHouse Value*Remaining Equity
0$200,000$0$0$800,000$600,000
1$215,000$15,000$15,000$824,000$609,000
2$231,125$16,125$31,125$848,720$617,595
3$248,459$17,334$48,459$874,182$625,723
4$267,094$18,634$67,094$900,407$633,313
5$287,126$20,032$87,126$927,419$640,293
6$308,660$21,534$108,660$955,242$646,582
7$331,810$23,150$131,810$983,899$652,089
8$356,696$24,886$156,696$1,013,416$656,720
9$383,448$26,752$183,448$1,043,819$660,371
10$412,206$28,759$212,206$1,075,133$662,927
Final (15)$591,775-$391,775$1,246,374$654,599

*House value assumes 3% annual growth from initial value of $800,000

Real-World Case Studies

Case Study 1: Margaret, Age 70

Initial Situation:

  • • Home value: $650,000
  • • Reverse mortgage: $200,000 at 7.2%
  • • Age: 70 years old
  • • Location: Wellington

After 12 Years (Age 82):

  • • Loan balance: $458,000
  • • Total interest added: $258,000
  • • Home value (4% growth): $1,038,000
  • • Remaining equity: $580,000

Outcome: Despite the loan more than doubling, Margaret still has substantial equity due to strong house price growth. Her initial $450,000 equity became $580,000.

Case Study 2: Robert, Age 75

Initial Situation:

  • • Home value: $800,000
  • • Reverse mortgage: $350,000 at 8.1%
  • • Age: 75 years old
  • • Location: Auckland

After 15 Years (Age 90):

  • • Loan balance: $1,133,000
  • • Total interest added: $783,000
  • • Home value (2% growth): $1,077,000
  • • Remaining equity: -$56,000 (protected)

Outcome: The loan exceeded the home value, but the no-negative-equity guarantee means Robert's estate owes only the home's value ($1,077,000), not the full loan balance.

Case Study 3: David & Susan, Ages 68 & 65

Initial Situation:

  • • Home value: $900,000
  • • Reverse mortgage: $270,000 at 7.8%
  • • Ages: 68 & 65 (LVR based on younger)
  • • Location: Christchurch

After 18 Years:

  • • Loan balance: $1,024,000
  • • Total interest added: $754,000
  • • Home value (3.5% growth): $1,736,000
  • • Remaining equity: $712,000

Outcome: Even after 18 years and nearly $800,000 in compound interest, the couple retained significant equity due to strong property appreciation.

Key Insights About Compound Interest

The Power of Time

  • • First 5 years: Interest grows slowly
  • • Years 10-15: Acceleration becomes noticeable
  • • After 15 years: Dramatic compounding effect
  • • Every extra year significantly increases debt

Interest vs Principal

  • • By year 10: Interest often equals original loan
  • • By year 15: Interest typically 2-3x original loan
  • • By year 20: Interest can be 4-5x original loan
  • • Total debt becomes primarily interest

House Price Growth Impact

  • • 4%+ annual growth usually preserves equity
  • • 2-3% growth may barely keep pace
  • • Below 2% growth can be problematic
  • • Location and market conditions matter hugely

Risk Factors

  • • Higher interest rates accelerate growth
  • • Larger initial loans compound faster
  • • Longer time periods create exponential effects
  • • Market downturns can be devastating

Bottom Line

Compound interest is a double-edged sword. While it allows you to access your home's equity without monthly payments, it can significantly erode that equity over time. The key factors are:

  • • How long you live in the home
  • • Interest rates during that period
  • • How much your property appreciates
  • • The size of your initial loan

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