In a low inflation world firms tend to raise prices once a year, typically in the first quarter of the calendar year or their fiscal year. Because of this very strong seasonal pattern, on a not seasonally adjusted around 50% of the annual increase in the core CPI — excluding food and energy — occurs in the first quarter
This very strong pattern gives great insight in to the annual inflation rate. One, is if this year’s first quarter is greater than or less that the prior year’s first quarter, this year’s annual increase will be greater of less than the prior year’s annual increase. This has worked every since year since 1990. Second, just doubling the NSA first quarter rate gives you an amazingly accurate estimate of the annual increase in the core CPI for that year. In 2018 the first quarter rose 1.20% and the annual increase was 2.16%. This year the first quarter rose 1.06%. This implies that the rise in the core CPI should be slightly less in 2019 than it as in 2018.