What is CPI-U?

The Consumer Price Index (CPI) is the statistical metric developed by the Bureau of Labor Statistics used to monitor the change in the price of a set list of products. The idea is that by monitoring the fluctuations in price it costs to purchase a set basket of goods, the government can track the cost of living for most individuals. The CPI-U is the CPI value for Urban Consumers, which excludes rural populations and represents approximately 80% of the population. The CPI and CPI-U do not directly measure inflation, but it gives a very good idea of whether we are in a period of inflation or deflation and how severe that change may be. As the Bureau of Labor Statistics states, "The CPI is generally the best measure for adjusting payments to consumers when the intent is to allow consumers to purchase at today's prices, a market basket of goods and services equivalent to one that they could purchase in an earlier period."

Many argue that the CPI-U is not a very good measurement of inflation in today's society. The CPI-U excludes the cost of energy and food, which have steadily risen over time. The basket of goods was defined before most of the modern technological revolutions had taken place, so the CPI-U does not account for electronics, computers,  or other standard household items today. Regardless, the CPI-U is the metric used by the Treasury for calculating the inflation-linked rate of an I Bond.

CPI-U Measurements

This table shows the CPI-U changes since 1998, when I Bonds were first released. I Bonds use the change in these numbers to determine the inflation-linked portion of the bond's rate. Bonds released in November through April use the CPI-U change from March to September. Bonds purchased between May and October use the CPI-U changes from September of the previous year through March.

Year	Jan.	Feb.	Mar.	Apr.	May	Jun	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.
1998	161.6	161.9	162.2	162.5	162.8	163.0	163.2	163.4	163.6	164.0	164.0	163.9
1999	164.3	164.5	165.0	166.2	166.2	166.2	166.7	167.1	167.9	168.2	168.3	168.3
2000	168.8	169.8	171.2	171.3	171.5	172.4	172.8	172.8	173.7	174.0	174.1	174.0
2001	175.1	175.8	176.2	176.9	177.7	178.0	177.5	177.5	178.3	177.7	177.4	176.7
2002	177.1	177.8	178.8	179.8	179.8	179.9	180.1	180.7	181.0	181.3	181.3	180.9
2003	181.7	183.1	184.2	183.8	183.5	183.7	183.9	184.6	185.2	185.0	184.5	184.3
2004	185.2	186.2	187.4	188.0	189.1	189.7	189.4	189.5	189.9	190.9	191.0	190.3
2005	190.7	191.8	193.3	194.6	194.4	194.5	195.4	196.4	198.8	199.2	197.6	196.8
2006	198.3	198.7	199.8	201.5	202.5	202.9	203.5	203.9	202.9	201.8	201.5	201.8
2007	202.416	203.499	205.352	206.686	207.949	208.352	208.299	207.917	208.490	208.936	210.177	210.036
2008	211.080	211.693	213.528	214.823	216.632	218.815	219.964	219.086	218.783	216.573	212.425

The below table shows changes in CPI-U as a percentage, which is what is used in the I-Bond rate calculation.

CPI-U Rate History
1-Nov-08	2.46%
1-May-08	2.42%
1-Nov-07	1.53%
1-May-07	1.21%
1-Nov-06	1.55%
1-May-06	0.50%
1-Nov-05	2.85%
1-May-05	1.79%
1-Nov-04	1.33%
1-May-04	1.19%
1-Nov-03	0.54%
1-May-03	1.77%
1-Nov-02	1.23%
1-May-02	0.28%
1-Nov-01	1.19%
1-May-01	1.44%
1-Nov-00	1.52%
1-May-00	1.91%
1-Nov-99	1.76%
1-May-99	0.86%
1-Nov-98	0.86%
1-Sep-98	0.62%

CPI-U Calculators

Based on the values of CPI-U, this calculator lets you determine the variable rate for an I-bond. November I bonds use the change in CPI-U from March to September. May I bonds use the change from September of the previous year to March.

November I-Bond March CPI-U September CPI-U CPI-U Increase	May I-Bond September CPI-U March CPI-U CPI-U Increase
Use this calculator to find the rate of an I-bond given the above CPI-U increase and the fixed rate of the bond. I Bond Rate Calculator CPI-U Increase in % Fixed Rate in % New I Bond Rate would be:

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