Opening a LEGO set roughly halves what it would sell for. In our market data, a used copy is worth a median of 0.52 times a sealed one, across the 451 sets that have both values. That matters only if you might sell: a set bought to build loses nothing you care about when you open it.

Quick answer: build what you bought to build. Keep a set sealed only if you are likely to sell it, and expect a used copy to be worth about half. The gap is wider for big and old sets. A second sealed copy rarely pays for both.

What our market data shows

We took every set in our catalog with both a new, sealed value and a used value in our market data: 451 sets, after dropping four whose two values looked mismatched. Most were checked between November 19 and 26, 2025, a handful during 2026. For each we divided the used value by the sealed value.

Group Sets Median used value, as a share of sealed
All sets 451 0.52
Worth under $50 sealed 177 0.62
Worth $50 to $150 sealed 132 0.50
Worth $150 to $400 sealed 95 0.50
Worth $400 or more sealed 47 0.40
Released before 2010 177 0.39
Released 2010 to 2019 144 0.52
Released 2020 or later 130 0.83

No set in the sample had a used value above its sealed value. Two patterns stand out. The more a set is worth sealed, the bigger the share opening takes away. And age widens the gap: a recent set that is still widely available new loses less, probably because a buyer can still get a sealed copy at or near list price. These are market estimates for a complete set, not sale prices for any one copy, and a used set missing pieces or its instructions is worth less again.

Condition, from best to worst

Buyers and price guides rank condition in roughly this order, each step worth less than the one before:

  1. Sealed, box in mint condition.
  2. Sealed, box creased, dented or faded.
  3. Opened, bags still sealed.
  4. Built, complete, with box and instructions.
  5. Built, complete, without box or instructions.
  6. Incomplete.

Our data only separates sealed from used, so we do not put a number on each step.

Does buying two copies pay?

The idea is to buy two copies, build one and sell the sealed one later for enough to cover both. The arithmetic is harder than it sounds. Bought at list price, two copies cost twice list. After selling fees and shipping of about 15%, the sealed copy has to sell for roughly 2.35 times list to cover both.

Of the 449 sets in our market data that retired from 2022 through 2025, 16 had reached that level. About half, 232 sets, had reached the much lower bar of breaking even on a single copy after fees, around 1.18 times list. So a second sealed copy usually offsets part of the cost of the first rather than paying for it. It works best when you pay well below list for both copies. Our guide to whether LEGO sets are a good investment in 2026 has the full figures by retirement year, theme and price.

When opening costs you nothing that matters

  • You bought it to build. The value you give up is resale value you never meant to use.
  • It is a gift for someone who will build it.
  • It is a small set. Half of a small sealed value is a few dollars, often less than postage.
  • It is still widely sold new. Recent sets lose the least when opened, and a sealed copy is easy to buy later if you change your mind.

Keeping a sealed set in good condition

  • Cool and dry: avoid attics, hot garages and damp basements. LEGO warns that heat can change the shape of bricks, and damp warps boxes.
  • Dark: sunlight fades box art.
  • Off the floor and lightly stacked: heavy stacks crush the boxes underneath.
  • Away from pets and price stickers: both mark the box.

The honest answer

For most people the right move is to open the set and build it. Keep a set sealed when you genuinely expect to sell it, ideally one bought below list, and treat the box as part of what you are selling. If you want the numbers on which sets have gained value after retiring, start with our 2026 investment guide, then the most valuable LEGO sets ever made and whether minifigures increase in value.

Figures come from our market data: sealed and used values for 451 sets, most checked in late November 2025, and current values against US list price for sets retired from 2022 through 2025. They describe the past, not a forecast.