Variable interest rate 0.8% → 1.4%? I quietly calculated whether our home mortgage will collapse.

Recently, every time I see news about interest rates rising, I feel a slight unease deep in my chest. When words like “It might go up again in December” circulate, something in our household budget quietly trembles.

Our home mortgage is a variable interest rate of 0.8%, a remaining balance of 30 million yen, and principal-equal repayment. It is a combination where the impact of interest rate hikes appears “most directly”.

That is precisely why I sat down and laid out the numbers properly.

■ A 0.6% increase = 180,000 yen per year. That is genuinely painful for a household.

What would happen if the interest rate rose from 0.8% to 1.4% (+0.6%)?

30 million yen × 0.6% = 180,000 yen per year. That comes to an increase in fixed costs of about 15,000 yen per month.

Looking only at the numbers, some might think, “Isn’t that just a rounding error?” But from a household perspective, a 15,000 yen monthly increase in fixed costs is genuinely painful.

Moreover, our household uses principal-equal repayment. Unlike principal-and-interest equal repayment, there is no grace period where “the repayment amount remains unchanged for five years.” The moment the interest rate rises, the repayment amount jumps immediately.

This “direct hit” feeling is unique to principal-equal repayment.

■ Principal-equal repayment has major benefits. But interest rate hikes hit directly.

With principal-equal repayment, the principal decreases rapidly in the early stages. It eliminates the weaknesses of variable interest rates, and the total repayment amount is lower. In the long term, it is a very rational repayment method.

However, it is a different story when interest rates rise.

With principal-and-interest equal repayment, there is a “grace period” where “the repayment amount remains unchanged for five years (the 5-year rule)”.

But with principal-equal repayment, an interest rate hike equals an immediate increase in repayment amount.

This difference is quite significant for a household.

■ Furthermore, there is a very real possibility that it will rise even further from here.

The interest rate environment in 2026 is influenced by:

• The Bank of Japan’s policy shift

• Rising long-term interest rates

• Continued high prices

• The trend of wage increases

These are overlapping.

Therefore, there is no guarantee that it will stop at 0.8% → 1.4%.

The possibility of it rising to 1.6% or 1.8% is not zero either. Variable interest rates are ‘it might go up, or it might not.’ This ‘fluctuation’ creates anxiety.

■ The 5-year rule and 125% rule could also lead to ‘a big loss if you are unlucky’.

Variable interest rates have mechanisms to prevent repayment amounts from jumping suddenly in place.

They are

At first glance, it looks reassuring, but there are actually pitfalls.

While the repayment amount does not increase, a period occurs where only interest increases and the principal does not decrease.

In other words, there is a possibility that you are losing money in ways you cannot see.

If you are unlucky, a ‘5 to 10-year period where the principal hardly decreases’ can occur.

Many people choose variable interest rates without knowing about this mechanism.

■ That is precisely why you should be cautious about rushing into early repayments.

When interest rates rise, many people panic and think, ‘I have to make an early repayment!’

But I am on the cautious side.

The reason is simple: early repayment tends to be an act that cuts into the ‘margin of the household budget’. because of that.

Child-rearing households have many unexpected expenses. Repair costs also add up. The peak of education expenses is also yet to come.

When the cash on hand decreases, the household budget loses its ‘escape route’.

Therefore, there is no need to rush into early repayment.

■ It’s a tough choice between variable and fixed, but I’m sticking with variable.

Fixed interest rates are safe. Variable interest rates are risky.

This is often said, but I am going with the variable rate.

The reason is, because it can be absorbed by the structure of our household finances.

• Keeping fixed costs low

• Small fluctuations in living expenses

• Knowing the peak of education expenses

• Setting aside repair costs separately

• Reducing principal early with equal principal payments

In other words, our household structure is built to absorb the ‘sway’ of interest rate hikes.

I believe it is more important to organize the margin in your household finances than to be swayed by interest rate fluctuations.

■ Conclusion: Interest rate hikes are the time to review your ‘household margin’.

When interest rates rise, you feel anxious. But that anxiety is also a chance to organize your household margin.

Just by reviewing these, you can absorb the sway of interest rate hikes.

■ A quiet final thought.

Interest rates are like a mirror that quietly reflects the habits of a household budget. When you feel anxious, it is time to quietly review the margins in your household finances.