Mortgage And Household Finance Series
This series looks at mortgages not from the standpoint of “how much can I borrow,” but from household cash flow and risk management.
- Flat 35 Tops 3% for the First Time
- Comparing Fixed and Variable Rate Scenarios for a 50 Million Yen Mortgage
- Mortgage Repayment Ratios by Income
- How to Calculate a Mortgage Amount That Is Harder to Break Your Household Budget
- Is Mortgage Prepayment Really Worth It? Should You Keep Cash or Repay Early? (this article)
- Is a Mortgage an Asset or a Liability?
- Using the New NISA While Carrying a Mortgage
- How to Avoid Buying “Negative Property”
[Summary]
After taking out a mortgage, many households begin thinking about prepayment.
They want to reduce principal, lower interest, and feel less burdened by debt.
That is natural.
But prepayment is not always the right answer. Mortgage rate, group credit life insurance, emergency funds, education costs, investment opportunities, mortgage tax benefits, and future rate risk should all be considered.
For a low-rate mortgage, prepayment is close to earning a guaranteed return equal to the mortgage rate. Keeping cash, however, preserves flexibility for unexpected expenses and long-term investment.
This article explains the two main prepayment methods, why liquidity matters, and a simple comparison between prepaying 10 million yen and investing it.
This is not a recommendation to prepay or invest. Investments can lose principal, and mortgage terms, tax rules, insurance, deductions, fees, and household conditions differ.
Prepayment as a “Guaranteed Return”
The benefit of prepayment is that it reduces future interest on the repaid principal.
This is similar to reducing expenses with a return close to the mortgage rate.
If a household prepays 1 million yen on a 0.5% mortgage, the rough annual interest reduction is about 5,000 yen. At 3.0%, the annual interest reduction is about 30,000 yen.
| Mortgage rate | How prepayment looks |
|---|---|
| Around 0.5% | Interest reduction is small; compare with liquidity and investment opportunities |
| 1.0% to 2.0% | Decision depends on household situation and rate-rise risk |
| Over 3.0% | Guaranteed interest reduction becomes much more meaningful |
Prepayment is not bad. But the lower the mortgage rate, the higher the opportunity cost of losing cash.
Shortening the Term vs Reducing the Monthly Payment
| Method | Mechanism | Better suited for |
|---|---|---|
| Term-shortening | Monthly payment stays the same; repayment period becomes shorter | Reducing total interest |
| Payment-reduction | Term stays the same; monthly payment decreases | Reducing monthly fixed costs |
The term-shortening method generally reduces total interest more.
The payment-reduction method improves monthly cash flow immediately. It can be more suitable when education costs are rising, one income may disappear, or the household wants protection against income decline.
Before prepaying, decide whether the goal is to reduce interest or reduce monthly fixed costs.
Three Reasons to Keep Cash
Investment Opportunities
When a mortgage rate is around 0.5%, the interest reduction from prepayment is limited.
Long-term diversified investing may be expected to earn more than the mortgage rate, for example through equity index funds.
But investment returns are not guaranteed. Markets can fall sharply. Prepayment is close to certain interest reduction; investment returns are uncertain.
Group Credit Life Insurance
Many Japanese mortgages include group credit life insurance. If the borrower dies or meets specified severe disability conditions, the remaining loan can be repaid by insurance.
If principal is prepaid, the insured balance also falls.
If cash is kept instead, and the insured event occurs, the loan may be repaid while the cash remains for the family.
Coverage differs by contract, illness type, exclusions, premium structure, and rate add-ons.
Liquidity
Cash can be used immediately.
Education, illness, job changes, caregiving, car replacement, and home equipment failures all require cash.
Money used for prepayment cannot easily be pulled back out. If early repayment makes cash thin and the household later uses high-interest debt, the prepayment has backfired.
Prepaying 10 Million Yen vs Investing It
Assume:
Mortgage balance: 30 million yen
Remaining term: 30 years
Mortgage rate: 0.5%
Excess cash: 10 million yen
Repayment method: Equal principal and interest| Method | Approximate effect |
|---|---|
| Payment-reduction prepayment | Total interest reduction of about 770,000 yen; monthly payment falls by about 30,000 yen |
| Term-shortening prepayment | Total interest reduction of about 1.32 million yen; term shortens by about 10.5 years |
If the 10 million yen is invested for 30 years at an assumed 4% annual return:
10 million yen × 1.04^30 = About 32.43 million yenThis looks powerful, but 4% is an expectation, not a promise. The new NISA has annual and lifetime contribution limits, so 10 million yen cannot necessarily be put into the tax-free account all at once.
The investment case only looks favorable if low mortgage rates continue, long-term investing can be maintained, and the investor can avoid selling during downturns.
When Prepayment Is Easier to Prioritize
| Situation | Reason |
|---|---|
| Mortgage rate is high | Guaranteed interest reduction is larger |
| Loan remains after retirement | Lowering old-age fixed costs matters |
| Investment volatility is hard to tolerate | Debt reduction may fit better than uncertain returns |
| Cash reserves are already sufficient | Prepayment can be made after protecting emergency funds |
| Debt causes strong psychological stress | Household management may become easier |
For fixed-rate loans above 3%, prepayment becomes a much stronger option.
When Keeping Cash Can Be Reasonable
| Situation | Reason |
|---|---|
| Mortgage rate is low | Interest reduction is small relative to the value of cash |
| Emergency funds are thin | Unexpected expenses become dangerous |
| Education costs will rise | Cash flexibility is valuable |
| Insurance coverage is strong | Keeping loan balance can retain protection |
| Long-term investing can be continued | Investment optionality remains |
Keeping cash does not mean spending it.
If the money is not prepaid, it should be separated into emergency funds, education funds, or investment funds.
Decision Order
1. Is the emergency fund sufficient?
2. Are large education or life expenses coming?
3. What is the mortgage rate?
4. What does the insurance coverage provide?
5. Will the loan remain after retirement?
6. Can the household tolerate investment volatility?If emergency funds are insufficient, cash comes before prepayment.
If the rate is high and the loan remains after retirement, prepayment becomes more attractive.
If the rate is low, cash is ample, and long-term investing is realistic, keeping funds can be reasonable.
Paying Early Is Not Always the Only Correct Answer
When mortgage rates were 5% or 6%, prepayment had enormous value.
Today, low-rate mortgages, group credit life insurance, the new NISA, and long-term diversified investing make the decision more nuanced.
The question is how the mortgage fits into the whole household balance sheet.
Prepayment buys peace of mind and reduces debt. Keeping cash preserves liquidity and investment optionality.
Both have merits and risks.
The next article asks whether a mortgage is an asset-building tool or a liability that constrains the household.
Sources
- Japan Housing Finance Agency, “Prepayment for Individual Housing Loans”
- Japan Housing Finance Agency, “Group Credit Life Insurance System”
- Japan Housing Finance Agency, “Repayment Change Simulation”
- Government Public Relations Online, “What Is NISA?”