Index methodology
Every number below is published on purpose. An index is only useful if you can see exactly how it's built.
What an index is
An index tracks a basket of LEGO sets as a single number over time. Each index starts at a base level of 1000 on its inception date; from there the level rises and falls with the combined value of its constituents. A level of 1100 means the basket is up 10% since inception; 950 means down 5%. It is the same idea as the S&P 500 — a way to see how a whole market is moving, not just one item.
What value we use
We value each set at its used-market price — the price copies actually change hands at on the secondary market, which is the number collectors care about. New-in-box and original MSRP are shown as context on set pages but are not what the index level tracks. Values are in US dollars.
Weighting
Our flagship indices are equal-weighted: every set in the basket counts the same, so the index reflects how the typical set is doing rather than being dominated by one expensive grail. (A later version will also offer weighting by how widely a set is held across real collections — a measure only a platform with a collection database can compute.)
Rebalancing & the divisor
Membership is reviewed on a fixed schedule (quarterly) by transparent rules — for example, the CollectORbuild LEGO 100 holds the 100 highest-value sets. When the basket changes, we recompute an internal divisor so that the composition change itself does not move the level: the index is continuous across a rebalance, and only real price movement changes it. This is standard index practice and the single most important safeguard against a misleading jump.
Data & updates
Levels are computed once daily from that day’s used-market values. Historical points are drawn from our price history. Market values are currently sourced from BrickPicker; as CollectORbuild’s own marketplace generates real sales, indices will move to being anchored on our own transaction data.
Indices currently cover LEGO sets. Parts and minifigures will be added once a compliant price source for them exists. Market values via BrickPicker. This is informational data, not investment advice.