Is Inflation Speeding Up Again, or Is It Just Gas Prices?
Gas got pricier in September, with the government’s weekly survey putting the average pump price at $4.36 a gallon, 7.3% more than in August. The prices underneath the headline (rent, services, most goods) held a 2.4% annual pace through August, and Wednesday’s Consumer Price Index from the Bureau of Labor Statistics, due at 8:30 AM ET on October 14, shows whether that changed. The same report fixes next year’s Social Security raise, which on our calculation from the official formula is already at least 3.4% unless prices drop by more than about 0.1% in September.
Three numbers before the September CPI report
On this page
- What happened to gas prices in September
- What the report means for the 2027 Social Security raise
- What rent and services say about lasting inflation
- The August report in brief
- Forecasts, and how the annual rate is rounded
- The Federal Reserve on energy prices
- The lines to read at 8:30 on Wednesday
- How we calculated
- Frequently asked questions
What happened to gas prices in September
Gas got a good deal more expensive in September. The U.S. Energy Information Administration’s survey of regular gasoline put the monthly average at $4.355 a gallon, up from $4.058 in August and $3.166 in September 2025, which is 7.3% more than a month earlier and 37.6% more than a year earlier. It was the highest monthly average since May, when the price hit $4.479. For a household that buys 50 gallons a month, a round number we picked for illustration, that is about $14.85 more in September than in August.
The climb came in the middle of the month. The weekly readings went from $4.157 on September 7 to $4.319 on September 14 and $4.478 on September 21, then held at $4.465 on September 28. By October 5 the price had eased to $4.354, which matters for October’s report, though September’s average is already set.
Show the data
| Category | Value |
|---|---|
| Jan | $2.81 |
| Feb | $2.91 |
| Mar | $3.64 |
| Apr | $4.10 |
| May | $4.48 |
| Jun | $4.05 |
| Jul | $3.93 |
| Aug | $4.06 |
| Sep | $4.36 |
A jump of that size is not common. In StockTitan’s copy of the weekly pump price series, a month over month rise in the average of 7.3% or more happened in 17 of the 141 months from January 2015 to September 2026, September included.
The pump price is a decent guide to the gasoline line in the CPI, although the two are measured separately, by different people and samples. In the six months from March to August 2026 the CPI gasoline index before seasonal adjustment moved in the same direction as the EIA monthly average every month, and the gap between the two changes was never wider than 1.7 percentage points (we compare them month by month in the chart below). Six months is a short record, but it makes the 7.3% rise at the pump a useful public clue to the CPI’s gasoline line before Wednesday.
Show the data
| Category | EIA pump price, monthly average | CPI gasoline, unadjusted |
|---|---|---|
| Mar | 25.1% | 24.9% |
| Apr | 12.8% | 11.1% |
| May | 9.2% | 8.6% |
| Jun | -9.6% | -9.7% |
| Jul | -2.9% | -2.1% |
| Aug | 3.2% | 2.5% |
Gasoline made up about 3.85% of the CPI basket in August, by our update of the July weight in the BLS August release, Table 1, so if the CPI gasoline index rose by the same 7.3% before seasonal adjustment, gasoline alone would add about 0.28 percentage point to the month’s overall price change. That is a calculation and not a forecast, since the CPI keeps its own sample and its own timing within the month.
The seasonally adjusted number that makes the headline can come out bigger still. Seasonal adjustment strips out the price swings that recur every year. In September 2025, a 1.1% rise in the unadjusted gasoline index turned into a 3.6% rise in the seasonally adjusted one. Airline fares, which depend on jet fuel, were up 23.4% over the year to August, a story we looked at in why plane tickets cost so much more this holiday season.
What the report means for the 2027 Social Security raise
Wednesday’s report is the last piece of the formula for next year’s Social Security cost of living adjustment, and the July and August numbers already put that raise at 3.4% or more unless CPI-W, the index it uses, falls by more than about 0.12% in September. The rule is written out by the Social Security Administration: "A COLA effective for December of the current year is equal to the percentage increase (if any) in the CPI-W from the average for the third quarter of the current year to the average for the third quarter of the last year in which a COLA became effective." The result is rounded to the nearest tenth of a percent.
CPI-W is a version of the index built on the spending of households that live mainly on wages, and it runs close to the headline number (3.5% over the year to August, against 3.4% for the all items index). Its third quarter 2025 average was 317.265, from the monthly values of 316.349, 317.306 and 318.139 on the BLS CPI-W series. For 2026 the July value is 327.104 and the August value 328.481, so only September is missing. If September merely matched August, the quarter would average 328.022, which is 3.39% above the 2025 average and rounds to a 3.4% raise.
| September CPI-W change from August, before seasonal adjustment | Social Security raise this produces, rounded |
|---|---|
| A fall of more than about 0.12% | 3.3% or lower |
| From a 0.12% fall to a 0.17% rise | 3.4% |
| From 0.17% to 0.46% | 3.5% |
| From 0.46% to 0.75% | 3.6% |
| From 0.75% to 1.04% | 3.7% |
For a sense of scale, CPI-W rose 0.26% from August to September 2025 before seasonal adjustment, a pace that would land in the 3.5% row. The table is our arithmetic from the SSA rule and the published index values, so the number that counts is the one SSA computes from Wednesday’s CPI-W, and it applies to benefits starting with the December 2026 payment that arrives in January 2027. For comparison, the raise paid in 2026 was 2.8%, according to SSA. On a hypothetical benefit of $2,000 a month, each tenth of a point is worth $2 a month, so a 3.4% raise would add $68 before any deductions.
What rent and services say about lasting inflation
Gasoline moves the monthly number, and housing, the biggest single weight in the index, is a large part of how long higher inflation sticks around. In the July 2026 weights that BLS publishes in Table 1 of the August release, shelter (mainly rent and what BLS calls owners’ equivalent rent) made up 35.3% of the basket, and gasoline 3.8%, so shelter weighs about nine times as much as gas.
Show the data
| Part | Value | Share |
|---|---|---|
| Shelter | 35.3% | 35.3% |
| Gasoline | 3.8% | 3.8% |
| Everything else | 60.9% | 60.9% |
Shelter has been calm. It rose 0.3% in August after 0.1% in July and was up 3.0% over twelve months, with rent up 2.7% and owners’ equivalent rent, the BLS estimate of what homeowners would pay to rent their own home, up 3.1%. Both have moved in small steps lately, between 0.1% and 0.3% a month from June to August on a seasonally adjusted basis.
The index for all items less food and energy, which economists call core inflation, carries that steadiness. It rose 2.4% over the year to August, down from 2.5% in July, while energy was up 16.3%. Inside core, prices of goods other than food and energy were up only 0.7% over the year, and services other than energy were up 3.0%. A few lines pull hard in opposite directions: airline fares rose 23.4% over the year and motor vehicle insurance fell 5.1%, while used cars and trucks were 2.3% cheaper than a year earlier.
Food sits in between. The food index rose 2.7% over the year, with groceries up 2.2% and meals away from home up 3.4%. Eggs rose 2.9% in August alone while lettuce fell 6.2%, the kind of swing that makes a shopping trip feel different from the statistics.
The reason this split matters is persistence. A price rise that comes from gasoline tends to reverse when fuel gets cheaper, as it did in June 2026, when the gasoline index dropped 9.7% and the all items index fell 0.4% in a single month. A rise that comes from rent and services tends to build over many months. The Fed’s minutes point to a third path, energy costs that stay high long enough to spread into other prices, which is why core services matter as much as rent. That reading is ours, and Wednesday’s core number is the first test of it for September.
The August report in brief
Prices rose 0.4% in August after 0.1% in July on a seasonally adjusted basis, and 3.4% over twelve months, the same annual rate as in July, according to the BLS release of September 11. BLS said "the index for gasoline rose 3.9 percent in August, accounting for over one third of the monthly all items increase."
The year has had two halves. The annual rate was 2.4% in January and February 2026, jumped to 3.3% in March when the gasoline index rose 21.2% in one month on a seasonally adjusted basis, peaked at 4.2% in May and has been at 3.4% or 3.5% since June. Core inflation never followed it up: it has stayed between 2.4% and 2.9% all year, and energy, up 16.3% over the year to August, is the main thing the core leaves out.
Show the data
| Category | All items | Core, without food and energy |
|---|---|---|
| Jan 2025 | 3.0% | 3.3% |
| Feb 2025 | 2.8% | 3.1% |
| Mar 2025 | 2.4% | 2.8% |
| Apr 2025 | 2.3% | 2.8% |
| May 2025 | 2.4% | 2.8% |
| Jun 2025 | 2.7% | 2.9% |
| Jul 2025 | 2.7% | 3.1% |
| Aug 2025 | 2.9% | 3.1% |
| Sep 2025 | 3.0% | 3.0% |
| Nov 2025 | 2.7% | 2.6% |
| Dec 2025 | 2.7% | 2.6% |
| Jan 2026 | 2.4% | 2.5% |
| Feb 2026 | 2.4% | 2.5% |
| Mar 2026 | 3.3% | 2.6% |
| Apr 2026 | 3.8% | 2.8% |
| May 2026 | 4.2% | 2.9% |
| Jun 2026 | 3.5% | 2.6% |
| Jul 2026 | 3.4% | 2.5% |
| Aug 2026 | 3.4% | 2.4% |
A 0.4% month is not unusual on its own. In StockTitan’s copy of the seasonally adjusted CPI series, a monthly rise at least as large as August’s (0.396% before rounding) came in 84 of the 438 months from January 1990 to August 2026, about one month in five. What stands out in 2026 is the path, a surge from March to May, a 0.4% fall in June, then a slow rebuild. BLS published no index for October 2025, so the chart above skips that month.
Wages give one more yardstick. Average hourly earnings of private sector workers rose 3.0% over the twelve months to September, according to the BLS employment report of October 2. The matching price figure for September arrives on Wednesday, when BLS also publishes its inflation-adjusted earnings for the month; the latest price figure, for the twelve months to August, was 3.4%.
Forecasts, and how the annual rate is rounded
Economists expect the monthly headline to speed up and the monthly core to slow down. As of October 9, the consensus compiled by Bloomberg had the CPI up 0.6% in September and 3.6% over twelve months, with core up 0.2% for the month and 2.5% over the year, and a poll by Reuters gave the same 3.6% and 2.5% for the annual rates. Those are forecasts by outside economists, and StockTitan makes none of its own.
How the annual rate gets from 3.4% to anything else is plain arithmetic. BLS computes it from the index before seasonal adjustment, compared with the same month a year earlier, so what matters is how September 2026 compares with September 2025. That month was mild: the unadjusted index rose 0.25% from August to September 2025, on the BLS all items series (324.800 against 323.976). For the unrounded annual rate to rise, September 2026 has to beat that pace, and the printed rate rises above 3.4% only if the month comes in above about 0.31%, while anything below about 0.21% would bring it down to 3.3% or lower.
| September 2026 change from August, before seasonal adjustment | Annual rate BLS would print |
|---|---|
| Below about 0.11% | 3.2% or lower |
| 0.11% to 0.21% | 3.3% |
| 0.21% to 0.31% | 3.4% |
| 0.31% to 0.40% | 3.5% |
| 0.40% to 0.50% | 3.6% |
| 0.50% to 0.60% | 3.7% |
The core rate is right on an edge. Over the year to August it was 2.446% before rounding, on the BLS core series, so it printed as 2.4%. Core rose 0.25% from August to September 2025 before seasonal adjustment, and it needs about 0.26% this September to print 2.5%, while anything under about 0.16% would take it down to 2.3% or lower. So a 2.5% print on Wednesday would not by itself mean core prices sped up, since last September’s pace, repeated, lands right on the line between 2.4% and 2.5%.
The Federal Reserve on energy prices
This is the last CPI report before the Fed’s next decision, at the meeting of October 27 and 28 on the Fed’s calendar. On September 16 the Fed raised its target range by a quarter point to 3.75% to 4%, and its statement said that "Inflation remains elevated." We covered that decision in the September rate hike.
The minutes of that meeting name energy directly. Participants said "ongoing geopolitical developments, which had pushed up prices for crude oil and refined fuel products, and surging AI-related investments were contributing to inflation pressures," and "many participants assessed that the longer energy prices remained elevated, the greater the risk that cost increases in certain sectors could lead to broader price pressures," according to the minutes released October 7. They also say "most participants assessed that another increase in the target range for the federal funds rate would likely be appropriate by year end." Our reading of those minutes covers the votes and the data calendar.
The Fed defines its 2% goal with a different index, the personal consumption expenditures price index, as its own explanation sets out. The CPI feeds into that measure, which is why officials and markets read it closely, but a CPI rate such as August’s 3.4% and the Fed’s 2% goal are not measured on the same yardstick.
The lines to read at 8:30 on Wednesday
The headline number will get the attention, and the lines beneath it say more about where prices go next. These are the ones we will read first when the report lands.
- How much of the monthly rise BLS credits to gasoline. In August it was "over one third." A share above half would mean most of the jump is fuel.
- Rent and owners’ equivalent rent. Readings back at 0.1% would say housing costs are still cooling, and readings of 0.4% or more would say the opposite.
- Services other than housing and energy, such as airline fares and car insurance. The minutes say several participants saw price increases in core services excluding housing that “remained elevated” (the Fed’s own inflation measure is PCE, not CPI).
- Core goods, where tariffs would show up, after a 0.7% annual rise in August.
- CPI-W, the index behind the Social Security raise, published in the same release.
Signs that higher prices are spreading would be a core rise of 0.3% or more alongside firmer shelter and services. Signs that the pressure is staying in fuel would be a big headline with core at 0.2% or less and shelter near 0.1% to 0.2%. Pump prices themselves, which slipped to $4.354 by October 5, point toward October’s report and not this one.
We will update this page with the official September figures shortly after 8:30 AM ET on Wednesday, October 14.
How we calculated
The annual rate thresholds come from the unadjusted CPI-U index: September 2025 (324.800) times one plus each rounding edge (3.15%, 3.25% and so on), divided by August 2026 (334.980). The core thresholds use the same method on the core series (330.804 and 338.041). The Social Security table solves the SSA formula for the September 2026 CPI-W value that puts the third quarter average at each rounding edge above the 2025 average of 317.265, then expresses it as a change from August’s 328.481. The boundaries in both tables are rounded for reading, and every calculation uses the unrounded index values.
The gasoline comparison divides the EIA monthly average of each month by the one before and sets it against the change in the unadjusted CPI gasoline index for the same months. The 3.85% weight is the July relative importance of 3.770 adjusted for the change in gasoline prices relative to all items between July and August. The count of large pump price rises and of 0.4% months uses StockTitan’s stored copies of the weekly gasoline series and the seasonally adjusted CPI index, queried on October 12, 2026.
Frequently asked questions
When is the September 2026 CPI report released?
The Bureau of Labor Statistics publishes it on Wednesday, October 14, 2026, at 8:30 AM Eastern Time, according to its October release calendar. The Producer Price Index for September follows on October 15.
What is the 2027 Social Security COLA going to be?
SSA computes it from the September CPI-W, so the official figure depends on Wednesday’s report. On our arithmetic from SSA’s formula and the July and August values, it comes to 3.4% if September CPI-W is between a 0.12% fall and a 0.17% rise from August, and 3.5% for a rise between 0.17% and 0.46%.
Why do gas prices affect the inflation rate so much?
Gasoline is only about 3.8% of the CPI basket, but its price moves far more than most items, sometimes 5% or 10% in a month. A 7% move in a 3.8% weight shifts the overall index by roughly a quarter of a percentage point, close to what the whole index rose in September 2025.
What is the difference between CPI and core CPI?
The CPI covers everything urban consumers buy. Core CPI leaves out food and energy, whose prices jump around, so it gives a steadier view of the trend. In August the CPI rose 3.4% over the year and core rose 2.4%.
How fast does 3.4% inflation cut the value of a dollar?
At a steady 3.4% a year, prices double, and a dollar buys half as much, in roughly 21 years by the Rule of 72 shortcut (72 divided by 3.4). You can try other rates with the Rule of 72 calculator.
Will StockTitan cover the CPI release?
Yes. StockTitan updates this article with the official September figures shortly after the 8:30 AM ET release on October 14.
Sources
- StockTitan: Fed minutes, September 2026
- StockTitan: Fed rate hike, September 16, 2026
- StockTitan: why plane tickets cost more
- Bureau of Labor Statistics: Consumer Price Index, August 2026
- Bureau of Labor Statistics: release calendar, October 2026
- Bureau of Labor Statistics: CPI-U all items, not seasonally adjusted
- Bureau of Labor Statistics: CPI-U all items less food and energy, not seasonally adjusted
- Bureau of Labor Statistics: CPI-U gasoline, not seasonally adjusted
- Bureau of Labor Statistics: CPI-W all items, not seasonally adjusted
- Bureau of Labor Statistics: Employment Situation, September 2026
- U.S. Energy Information Administration: retail gasoline prices, monthly
- U.S. Energy Information Administration: retail gasoline prices, weekly
- Social Security Administration: cost of living adjustment rule
- Federal Reserve: FOMC statement, September 16, 2026
- Federal Reserve: minutes of the September 15 and 16, 2026 meeting
- Federal Reserve: meeting calendar
- Federal Reserve: why the goal is 2% inflation
The information provided in this article is for educational and informational purposes only. It does not constitute financial advice, investment recommendation, or an endorsement of any particular investment strategy. Past performance does not guarantee future results. Investors should conduct their own research and consult with a qualified financial advisor before making investment decisions.