What if your mortgage interest rate goes from 1% to 2%? Monthly payments on 30 million yen increase by 15,000 yen! A thorough comparison by loan amount and remaining years

In November 2026, mortgage interest rate trends are once again in the spotlight.

According to the Housing Industry News dated November 13, while variable interest rates at major banks remained unchanged from the previous month, it is pointed out that mortgage interest rates may rise further due to future interest rate hikes.

For those paying off a mortgage, isn’t the monthly payment a concern?

“If the interest rate goes up by 1%, how much will the monthly payment increase?”

“Should I switch from a variable rate to a fixed rate?”

“Is it more cost-effective to make early repayments?”

In this article, we will organize these questions using concrete numbers.

1. Why do variable interest rates rise?

Variable mortgage interest rates are often set with reference to banks’ short-term prime rates and are influenced by the Bank of Japan’s policy interest rate.

When the Bank of Japan raises its policy interest rate, banks’ funding costs and other factors change, which may lead to an increase in mortgage interest rates.

However, just because the Bank of Japan raises interest rates by 0.25%, it does not mean that all mortgage interest rates will rise by 0.25% on the same day.

The actual applied interest rate varies depending on the financial institution and contract terms.

2. What changes between a 1% and 2% interest rate?

For example, suppose your mortgage balance is 30 million yen and the remaining repayment period is 35 years.

At 1% per annum, the monthly repayment is approximately 84,686 yen.

At 2% per annum, it is approximately 99,379 yen. This is an increase of about 14,693 yen per month.

Over one year, this results in an increased burden of approximately 176,000 yen.

Since mortgages are repaid over a long period, even a 1% difference in interest rates has a significant impact on household finances.

However, this is a simple model that recalculates the repayment amount when the interest rate changes. In actual variable rate loans, the rules for reviewing repayment amounts may differ.