I like collecting stamps. My grandmother got me started in 1969 with a six-cent stamp  honoring explorer John Wesley Powell, who went down the Colorado River through the Grand Canyon. Here’s a picture:
A few months ago, talked with a friend who is sorting his father’s old stamps. My friend observed that it costs a lot more to mail a letter these days. I agreed and filed that fact away. A few weeks ago, I read that the first-class letter rate increased from 58 to 60 cents. Wow, mailing a letter has risen by ten times since I started collecting in 1969!
I decided to quantify this rise using Postal Service data. I looked at what it cost to mail a one-ounce letter via first class mail from 1885 to 2022. I plotted the first-class postage rate versus time using a logarithmic scale; that makes it easier to view change over time. Note: You can scroll into this plot to see the dates and rates. The formatting and weird spacing after the plot – that’s due to my poor knowledge of WordPress.
I first noticed how flat the left side of the plot was. It cost two cents to mail a letter from 1885 to 1932 except for one interval around World War One; the rate was increased to three cents from 1917 to 1919. So, the rate stayed flat for most of 47 years.
The first long-term increase was from two to three cents in July 1932 during the Depression. This rise of 50%was a decision by the Hoover administration. Now, we might think it was just a penny but keep in mind that the value of a penny in 1932 was equal to about 21 cents in 2022. 
First-class postage jumped to 4 cents in August 1958; this was 26 years after the last increase. Another way to think about this is the doubling time, which was 73 years to double from 2 to 4 cents.
Our next doubling of rates from 4 cents to 8 cents happened in 1971, just 13 years. The plot is starting on an upward trend. The increase from six cents in 1969 to 8 cents in 1971 coincides with a significant change for the Post Office, which moved from a government department to an independent United States Postal Service as defined in the Postal Reorganization Act of 1970. President Nixon said: ““Our present postal system is obsolete; it has broken down; it is not what it ought to be for a nation of 200 million people.… And now is the time to act.“ My take is that you might want to hold on to your wallet when a President decides to tinker with the postal system. 
Our fastest doubling of postal rates took only seven years during the stagflation years of the 1970s, under the Nixon, Ford, and Carter administrations.  These were tough times for the United States; we experienced high inflation with high unemployment. Sadly, the 2020s look like they will mirror the 1970s.
We had another 13-year doubling period in 1991. The inflation-fighting of Fed Chairman Paul Volcker had tamed inflation. We reaped the benefits of lower inflation for the next 30 years; it took that long for postal rates to jump from 29 to 58 cents. The table below summarizes the doubling data, I have added a column for Consumer Price index (CPI) data as a reference.
|July 1, 1885||2||73.1||7.99|
|August 1, 1958||4||73.1||28.9|
|May 16, 1971||8||12.8||40.3|
|May 29, 1978||15||7.0||64.5|
|February 3, 1991||29||12.7||134.8|
|August 29, 2021||58||30.6||273.57|
Now, any bets on the time it takes for postage to double from the 58-cent rate of 2021? My best guess is seven years since we just entered what looks to be another period of epic inflation.
Notes and Sources
 “John Wesley Powell, the noted geologist who explored the Colorado River, was honored on a 6-cent stamp issued August 1, 1969. Powell led an 1869 expedition down the Green and Colorado Rivers, a 1,000-mile, four-months’ journey.” Image and text from US Bureau of Engraving and Printing via Wikipedia https://en.wikipedia.org/wiki/File:John_Wesley_Powell_1969.1.jpg accessed 25 July 2022
I should mention that the John Wesley Powell stamp made me realize I wanted to explore the Grand Canyon. I got my first look at the Grand Canyon, from he North Rim, in the summer of 1978. I have now hiked around and across many times. I still hope to raft the Colorado some day.
 The Consumer Price index (CPI) was 13.60 for July 1932. The CPI was 292.3 in May 2022. the ratio 292.3 / 13.6 is 21.5
Source U.S. Robert Shiller data set, Stock Markets 1871-Present and CAPE Ratio
 The Nixon quote is from Ryan Ellis, he provides a good description of the background behind the Postal Reorganization Act of 1970
The Birth of the USPS and the Politics of Postal Reform by Ryan Ellis accessed 25 July 2022
 Doubling the 8 cent rate of 1971 would require a 16 cent rate. I chose the closest rate of 15 cents in 1978, which isn’t quite double. I also chose 29 cents in 1991 as the next closest rate from 15 cents. While not perfectly accurate, I think they make the point.