I run Inflation Record, a small site that turns the US Consumer Price Index into calculators: what $100 in 1913 is worth today ($3,361.64, if you are curious), what a 2020 salary needs to be now, that kind of thing. The whole site is generated from one BLS series — CPI-U, monthly values from January 1913 onward.
Building it was mostly uneventful. Then the data itself started doing interesting things.
There is no CPI value for October 2025. The BLS did not publish one during the federal government shutdown, and no official value exists — not delayed, not estimated. Gone. My pipeline happily averaged the other eleven months of 2025 anyway, because code does what you tell it to. An eleven-month mean is a legitimate statistic, but only if the page says that is what it is. So now every annual average carries a count of how many months it actually contains, any year under twelve renders a visible note naming the missing month, and nothing is ever interpolated. A calculator that quietly invents an official statistic is worse than one with a hole in it.
The same honesty applies in miniature to the current year: the 2026 average covers January to September, so it is labelled "partial year" instead of pretending to be finished.
The site now covers four countries — the US, Canada, Australia and the UK — across 366 pages of year tables, calculators and data. Australia was the awkward one: its CPI history is three different products stitched across a century, and the build keeps those segments explicitly separate rather than smoothing them into a fake continuous line.