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The basic Excel formula for inflation is =New_CPI/Old_CPI-1. If the earlier CPI is in B2 and the later CPI is in B3, enter =B3/B2-1, then format the result as a percentage. For example, CPI values of 270.970 and 292.655 produce approximately 8.0% inflation.
The formula is simple; choosing the correct CPI observations is the important part. The appropriate comparison depends on whether you need month-over-month, year-over-year, annual-average, cumulative, or annualized inflation.
The inflation formula in Excel
Inflation is the percentage change in a price index between two periods:
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Inflation rate = (Later CPI − Earlier CPI) / Earlier CPIIn Excel, the equivalent formulas are:
=(New_CPI-Old_CPI)/Old_CPI=New_CPI/Old_CPI-1
With the earlier CPI in B2 and later CPI in B3:
=B3/B2-1The second version returns a decimal. Excel displays 0.08 as 8% after you apply percentage formatting.
CPI is an index measuring the average price level for a defined population, basket, geography, category, and reference base. It is not a dollar price and it is not itself an inflation rate. A CPI of 110 generally means prices are 10% above the index’s reference period, whose value is commonly set to 100; it does not mean inflation is 110%. See the BLS explanation of CPI and index values.
Example: calculate inflation between two CPI values
Set up a worksheet like this:
| Period | CPI | Inflation rate |
|---|---|---|
| Earlier period | 270.970 | |
| Later period | 292.655 | =B3/B2-1 |
The CPI increased by 21.685 index points. The inflation rate is:
=292.655/270.970-1That result is approximately 8.0%. The 21.685-point increase is not the percentage rate; it must be divided by the earlier CPI.
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- Select the formula cell.
- Go to Home → Number → Percent Style.
- Use the decimal-place buttons to display 0%, 0.0%, or 0.00%.
Use more decimal places only when they are justified by the precision and purpose of the underlying CPI data.
Calculate year-over-year inflation
For official 12-month inflation, compare the same month in consecutive years:
=Current_Month_CPI/Same_Month_Last_Year_CPI-1For example, comparing December values:
=296.797/278.802-1produces approximately 6.5%.
| Date | CPI | Year-over-year inflation |
|---|---|---|
| December 2021 | 278.802 | |
| December 2022 | 296.797 | =B3/B2-1 |
January-to-December is an 11-month interval, not a true same-month, 12-month comparison. December-to-December, March-to-March, and June-to-June are all 12-month comparisons. The BLS percentage-change guidance explains these distinctions.
Calculate month-over-month inflation
To measure the change from one month to the next, compare adjacent CPI observations:
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=Current_Month_CPI/Previous_Month_CPI-1| Month | CPI | Month-over-month rate |
|---|---|---|
| January | 300.000 | |
| February | 301.200 | =B3/B2-1 |
A month-over-month rate is not automatically an annual inflation rate. It describes only the interval between the two monthly observations.
Annualize a monthly inflation rate
If a monthly rate is in B2, the compounded annualized scenario is:
=(1+B2)^12-1For a monthly rate of 0.5%:
=(1+0.5%)^12-1This assumes the same monthly rate repeats for all 12 months. It is therefore a hypothetical annualized rate, not the official year-over-year inflation rate. For the latter, compare the current month’s CPI with the CPI for the same month a year earlier.
Calculate cumulative inflation
Using beginning and ending CPI values
For inflation over several years, use the first and last comparable CPI values:
=Ending_CPI/Beginning_CPI-1For example:
=325/250-1returns 30% cumulative inflation.
Using a list of annual inflation rates
Annual rates compound, so do not simply add them. If rates are in B2:B6, use:
=PRODUCT(1+B2:B6)-1In current Excel versions, this can normally be entered directly. For a more accessible layout, create a growth-factor column:
| Year | Inflation rate | Growth factor |
|---|---|---|
| 2021 | 4.7% | =1+B2 |
| 2022 | 8.0% | =1+B3 |
Then calculate:
=PRODUCT(C2:C3)-1=SUM(B2:B6) is only an approximation and becomes less accurate as rates increase.
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Calculate an inflation-adjusted amount
If you want to know what an earlier amount would equal in the later period, use the CPI ratio:
=Earlier_Amount*Later_CPI/Earlier_CPIFor example, to adjust $500:
=500*240.236/237.805This returns approximately $505.11. That is a purchasing-power adjustment, not an inflation-rate result. The related cumulative inflation rate is:
=240.236/237.805-1The BLS CPI math guide provides the same CPI-ratio approach for converting dollar amounts between periods.
Calculate annual-average inflation
Annual-average inflation compares the average of all 12 monthly CPI values in one year with the average of all 12 monthly values in another year. If 2024 values are in B2:B13 and 2023 values are in C2:C13:
=AVERAGE(B2:B13)/AVERAGE(C2:C13)-1A clearer worksheet is:
| Year | Annual average CPI |
|---|---|
| 2023 | =AVERAGE(C2:C13) |
| 2024 | =AVERAGE(B2:B13) |
Then compare the two averages with:
=B3/B2-1Annual-average inflation and December-to-December inflation are different measures. The first uses every month in both years; the second uses only two December observations. Neither should be substituted for the other without labeling the measure. See the BLS CPI questions and answers.
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For monthly data, use columns such as:
| Date | Year | Month | CPI | Prior-year CPI | YoY inflation |
|---|---|---|---|---|---|
| Actual Excel date | =YEAR(A2) |
=MONTH(A2) |
Index value | Lookup result | Percentage change |
- Sort the data chronologically.
- Check that dates are real Excel dates and that every needed month exists.
- Retrieve the CPI dated 12 months earlier.
- Divide the current CPI by that prior-year CPI and subtract 1.
Modern Excel: use XLOOKUP
If dates are in column A, CPI values in column B, and prior-year CPI in column C, enter:
=XLOOKUP(EDATE(A2,-12),$A:$A,$B:$B,"")Then calculate year-over-year inflation in column D:
=IF(C2="","",B2/C2-1)This date-based method is safer than assuming the row 12 positions earlier is always the same month.
Older Excel: use INDEX and MATCH
For editions without XLOOKUP, use:
=IFERROR(INDEX($B:$B,MATCH(EDATE(A2,-12),$A:$A,0)),"")If the dataset contains exactly one row for every month, a 12-row reference can work, but it can silently fail when a month is missing. Transparent helper columns are usually easier to audit than a volatile OFFSET formula.
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Excel does not have a universal built-in “inflation rate” function. You supply comparable CPI observations, and Excel calculates the percentage change.
For U.S. data, start with an official source such as the BLS CPI-U all-items U.S. city average series CUUR0000SA0:
BLS CPI-U all-items time series
You can download a file from the data provider or copy the relevant date and CPI columns into Excel. If a file is available, Data → From Text/CSV can import it. Government interfaces can change, so rely on the current labels shown by the provider rather than a fixed menu path.
Before calculating, verify:
- CPI-U or another population definition.
- All items or a specific category such as food, energy, shelter, or medical care.
- U.S. city average, a regional index, or a local-area index.
- Seasonally adjusted or not seasonally adjusted data.
- Monthly observations versus annual averages.
- A consistent index series and reference base.
BLS describes CPI coverage and methodology in its CPI overview and technical notes. The formula is universal, but the correct data series depends on the country and question.
Check imported data
Use these tests to identify values imported as text:
=ISNUMBER(A2)
=ISNUMBER(B2)The first checks a date and the second checks a CPI value. If a numeric value is stored as text, try:
=VALUE(B2)
=--B2Record the source, series ID, release date, and download date when the worksheet must be reproducible.
Common Excel mistakes
Forgetting -1
=New_CPI/Old_CPI returns a ratio such as 1.08, not an 8% inflation rate. Use:
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=New_CPI/Old_CPI-1Using the later CPI as the denominator
Percentage change is measured relative to the earlier value:
=(New_CPI-Old_CPI)/Old_CPIDividing by the later CPI answers a different question and is not the conventional inflation calculation.
Adding monthly or annual rates
Changes compound. Use matching CPI values for the desired interval, or use PRODUCT(1+rates)-1 when you have a series of rates.
Mixing CPI series
Do not compare CPI-U with another population, a U.S. city average with a local-area index, all-items CPI with a category index, or seasonally adjusted data with unadjusted data. The two observations must represent the same conceptual series.
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A CPI of 300 does not mean that the basket costs $300. CPI is an index. Use the ratio of two CPI values for percentage changes and purchasing-power adjustments.
Calling a personal experience “the CPI inflation rate”
CPI is an average measure. A household spending heavily on rent, gasoline, tuition, or health care may experience a different inflation rate from headline all-items CPI.
Quick Recap
Choose the calculation that matches the question
| Question | Use this method |
|---|---|
| How much did prices change from March to April? | Month-over-month CPI change |
| What was inflation over the last 12 months? | Same month year-over-year change |
| What happened during a calendar year? | Clearly labeled January-to-December interval or December-to-December comparison |
| What was the average inflation rate for a year? | Annual-average CPI comparison |
| What would $100 then equal today? | Original amount multiplied by the CPI ratio |
| What was the average yearly rate over a long period? | =(Ending_CPI/Beginning_CPI)^(1/Years)-1 |
| What is the combined effect of several annual rates? | =PRODUCT(1+rates)-1 |
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