[Definitive Guide] Investment Strategies to Grow Assets Even When Mortgage Rates Rise

“Variable rates have gone up again”—there must be many people who sighed this autumn after looking at their repayment schedules.

In October 2026, the variable interest rate at au Jibun Bank rose by 0.600% compared to the previous month, and Sony Bank rose by 0.500%. The average for seven online banks was 1.598%, an increase of 0.306% in just one month. Moreover, this only reflects the “June rate hike.” The September rate hike (policy rate from 1.00% to 1.25%, the highest level in about 31 years) is expected to affect new loans from December onwards through the raising of the short-term prime rate by major banks, and will affect existing loans starting from the July 2027 repayment.

Furthermore, over 80% of the market expects the “next rate hike to be in December.”

Right now, there are probably three things on the minds of people with mortgages:

・Should I rush to make early repayments, or should I continue with my new NISA?

・Should I switch from a variable to a fixed rate? (But fixed rates are as high as 3.6% to 4.7%)

・In a world where interest rates are rising, where can I put my assets to protect them?

I also struggled with this same situation. I wondered if I should keep buying stocks while I still have a loan balance. To conclude, the answer is determined almost mechanically by the “interest rate figures.” You can judge based on the break-even point, not by emotion.

■ Figures as of November 2026 (Source at the end of the text)

・Bank of Japan policy rate: 1.25% (Held steady at the 10/30 meeting; one dissenting vote proposed a rate hike to 1.50%)

・Variable interest rates: Mega bank average 1.332% / Online bank average 1.598% / Regional bank average 1.505% (October 2026)

・10-year fixed rate: Mega bank average 4.033% (Sumitomo Mitsui 4.750%)

・Flat 35: 3.83% in October (Rakuten Bank), expected to be in the high 3.5% range in November

・Interest rate gap between variable and fixed: Approximately 2.50% = equivalent to ten 0.25% rate hikes

・Long-term interest rate (10-year JGB): Around 2.885% (10/22). Briefly hit the 3% range in September

・Individual Government Bonds (Variable 10): Initial rate 2.05% (October offering)

■ The Truth Contrary to Conventional Wisdom

“If interest rates rise, pay off your mortgage early at all costs”—this is only half correct.

Making an early repayment on a variable-rate mortgage at 1.2% is the same as investing 1 million yen to turn it into approximately 1.27 million yen over 20 years. On the other hand, if you can invest that same 1 million yen at 4% per year for 20 years, it becomes approximately 2.19 million yen. The difference is over 900,000 yen.

Conversely, for a fixed-rate mortgage at 3.58%, early repayment is equivalent to an investment with a “guaranteed yield of 3.58%,” resulting in approximately 2.02 million yen after 20 years. This is a match almost on par with risk-taking stock investments.

In other words, the correct answer to “early repayment or investment” is the exact opposite depending on your mortgage interest rate.

■ What You Will Gain from This Article

1. “How high will variable rates go?” based on 3 policy interest rate scenarios

2. Repayment stress test table for a 35-million-yen, 35-year mortgage (interest rates 0.5% to 3.75%)

3. A decision formula to instantly determine the break-even point between early repayment and New NISA

4. 5 strategies to strengthen your asset side during a period of rising interest rates

5. Action plans by type (Variable / Fixed / Buying soon / Considering refinancing)

■ Bonuses (Inside the paid area)

Bonus 1: Repayment amount stress test quick reference table (save and use as-is)

Bonus 2: “Early repayment or investment?” decision flowchart (text version)

Bonus 3: 3 copy-paste prompts to calculate your own mortgage using AI

Bonus 4: Checklist for interpreting interest rate events (BOJ meetings, short-term prime rate, Flat 35 announcements)

Bonus 5: Follow-up update to refresh the numbers after the December BOJ meeting (purchasers can read it for free forever)

■ About Me

I am Kabushiki Taro, with 15 years of investment experience and a portfolio of over 200 stocks managed by AI. My job is to translate news about earnings, interest rates, and crude oil into the question, “So, what should I do with my holdings?” This article is a reorganized version of the decision-making table I created for myself, as I manage both a mortgage and asset investments.

■ Recommended for

・Those with a variable-rate mortgage who are worried about the December rate hike

・Those who cannot decide whether to put their money toward early repayment or the new NISA

・Those planning to buy a house soon and are torn between variable and fixed rates

■ Not recommended for

・Those who do not have a mortgage and have no plans to take one out in the future

・Those looking for buy/sell instructions for specific stocks (this article provides a framework for decision-making and does not recommend specific stocks)

■ About the price

It is 980 yen. With a 35 million yen loan, a 0.5% change in interest rates results in a monthly repayment difference of about 8,500 yen and a total repayment difference of about 3.6 million yen. I believe this is a sufficiently low price as insurance to avoid making a single wrong decision.

Furthermore, with a membership (Basic ¥500/month), you get unlimited access to all flagship features, including this article.

Now, let’s start by looking at “how high will variable interest rates go?” To give you the conclusion first, there is a possibility that it won’t end at the “additional 0.25%” that many people are assuming—