Sweden: the longest series here, and the flattest at its far end
Swedish consumer prices are recorded further back than for any other country on this site. Statistics Sweden's cost-of-living table starts in 1830, and this page will convert a sum from then without complaint. Two things are worth knowing before you trust the answer.
The first is frequency. Before July 1914 the series is annual only, so a figure from the 1870s rests on a single yearly observation rather than a run of monthly ones. The second is that very little happened. Prices rose about 59% across the eighty-four years to 1914, a little over half a percent a year, which is why a sum from 1850 converts to far less than most people expect. Swedish inflation is overwhelmingly a twentieth-century event: the same index rises roughly ninety-sevenfold between 1830 and 2025, and almost all of that comes after the First World War.
The index here is not the one the Riksbank targets
Sweden publishes two headline measures, and the gap between them is not academic. The KPI used on this page includes mortgage interest costs. The KPIF holds the interest-rate component fixed, and it has been the Riksbank's target variable since September 2017.
That difference has an awkward consequence. Raising the policy rate to slow inflation mechanically raises the mortgage interest sitting inside the KPI, so the measure moves up before it moves down. If you are checking this page against a Riksbank forecast or a newspaper's "Swedish inflation" figure, confirm which of the two is being quoted, because during a tightening cycle they can point in opposite directions.
Converting across 1992 crosses two monetary regimes
The change of regime is visible in the index itself. Between 1980 and 1990 the series roughly doubled, an average of about 7.6% a year. After the Riksbank abandoned the fixed exchange rate and let the krona float on 19 November 1992, and the inflation target followed, the next twenty-seven years added only about 38% in total, near 1.2% a year.
So a conversion from 1985 is dominated by the decade that follows it, not by the thirty years after. One thing that never interrupts the series: the krona has not been redenominated since it was introduced, and Sweden did not adopt the euro, so a Swedish amount from any year is already in today's unit.