Interest rates on fixed deposits in Osaka remained at '5%' for 37 months—yet the 'average' in the same table was moving
1. The Mystery
It is common for the interest rates on current fixed deposits to remain the same for many years.
In Osaka over 100 years ago, there was also a table where the same figure continued for over three years.
It is the ‘minimum’ column among the interest rates (annual % rate) applied to fixed deposits by Osaka banks.
For 37 months, the same 5.00% continued.
Did the interest rates on fixed deposits in Osaka really not move for three years?
The clue to the answer was in the adjacent column of the same table.
2. The Clue
The figures are in the ‘Monthly Table of Osaka Interest Rates’ (p. 119) in ‘Meiji Taisho Kokusei Soran’ (1927) by Toyo Keizai Inc.
Fixed deposit interest rates are written in three columns: ‘minimum’, ‘average’, and ‘maximum’.
Let’s look at the average and maximum columns for the same 37 months.
The average and maximum rose in the spring of 1908 and fell in the spring of 1909.
So, what happened in the spring of 1908 and 1909?
3. The Trick
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If you look at only one column and read it as ‘it didn’t move for three years,’ you will be mistaken. Even though the minimum column remained at 5.00, the average was moving: 5.50 → 6.00 → 5.00.
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The ‘minimum’ can be considered the figure for the bank that offered the lowest interest rate. Even if the lowest point did not move, the interest rates at other banks could rise or fall.
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The fact that the value remained the same for many months might not mean there were no numbers, but rather that someone had set it as a fixed rate. If you simply read it as ‘it didn’t move,’ you will overlook the reason.
4. The Truth (The answer and how to verify it)
Answer: Only the ‘minimum’ column did not move. It is believed that the average and maximum moved around the same time as 1908, when major banks in Tokyo raised interest rates on time deposits, and 1909, when they lowered them.
The chronology (p. 39) in the ‘History of the Bank of Japan: 100-Year History’ data volume contains the following two items:
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April 13, 1908: Commercial banks in Tokyo raised interest rates on deposits (major bank time deposits 5% → 6%)
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February 22, 1909: Commercial banks in Tokyo lowered interest rates on deposits (major bank time deposits 6% → 5%)
The average and maximum in Osaka rose in March 1908 and fell in March 1909. It is believed that banks in Tokyo and Osaka reviewed their interest rates around the same time.
This table does not reveal which bank offered the minimum of 5.00% or why it did not change.
How to verify:
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Used only figures from the original document that were verified through machine matching, cross-checking, and visual inspection (Verification mark: commercial table)
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Aligned the three columns of minimum, average, and maximum from the same table for the same month
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Visually verified the dates in the chronology against the original page (p. 39)
5. How to distinguish now (to avoid being deceived)
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Even if one column does not move, compare it with other columns in the same table (average, maximum) before saying ‘it didn’t move.’
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First, verify whether the number is the ‘minimum,’ ‘maximum,’ or ‘average.’
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If a value remains the same for many months, look for the person or rule that determines it.
Even current investment schemes that claim ‘stable at X% per year’ should look different if you compare them with other figures in the same table.
Next time, I will solve another mystery using figures from original documents.
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Source: National Diet Library Digital Collections, ‘Meiji Taisho Kokusei Soran’ (Toyo Keizai Inc., 1927, copyright expired), p. 119, ‘Osaka Monthly Interest Rate Table’.
https://dl.ndl.go.jp/pid/1269537/1/100
Bank of Japan, ‘One Hundred Year History of the Bank of Japan’, Materials Section, Chronology, p. 39.
https://www.boj.or.jp/about/outline/history/hyakunen/hyakus.htm
Please read this next (previous free installment):
Short-term lending interest rates in Tokyo increased 2.53 times in August 1916—what happened?
https://note.com/investad/n/nce3ad0145f13
※ This article introduces history and figures from that time. It does not recommend current interest rates or the buying and selling of specific financial products.
© 2026 Invest@D Konjiki Yasha. Unauthorized reproduction of the text, charts, and table structure is prohibited (citations are welcome if the source and URL are included). The figures themselves are from publicly available materials from the National Diet Library (copyright expired) and can be used by anyone.