Every Diamond Has a Half-Life

Updated October 2026. I first published this in July on three and a half months of prices. I've now re-run every number on the full season, rebuilt from scripts I can show you, and some of the July numbers were wrong. The main advice still holds: sell early. What changed:

• The decay is steeper than I said. A pack diamond that can actually fall loses about 26% in a week, not 7%. Most likely, July's curve looked gentle because I counted cards that launched already at their quick-sell price, which can barely fall.
• Earned cards fall about 1.4 times as fast as pack cards in week one, not 3 times. And some of the worst ones came back later in the season.
• The roster-update run-up was about +4%, not +99%. That section is rewritten.
• On flash-sale days the typical diamond was 5 to 12% lower, not 25 to 30%, and one of them didn't bounce.
• Two red days is not a reason to buy the dip. I called the sell rule "backwards". It's closer to a coin flip.

The rest of this post is the corrected version.

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The best moment to sell most Diamonds in MLB The Show has already passed. By the time you noticed the card was getting good, the people who notice these things for a living had already sold to you.

I used to think that was a vibe. Then I pulled the numbers: 468,197 daily price records, every card on the market, from March 17 to October 10. It's not a vibe. It's a decay curve, and it starts the day the card hits packs.

This is not advice for the floor. The floor is fine. This is advice for the cards in your inventory right now that you bought for two hundred thousand stubs, that are currently worth one hundred and twenty, and that you keep thinking will recover.

Most of them will not recover. Here's the proof, and here's what to do about it.

One rule before the data: pack cards

Most of what's below is about pack cards. I count a card as a pack card if it shows up on SDS's official pack odds and isn't itself a program or collection reward. (Some of them can also come out of packs a program hands you, so "pack" here means where the copies come from, not that you can never get one any other way.) Earned cards, the ones you grind out of an XP path, a program or a collection, are a different animal. My read is that when a wave of players finishes the grind, a wave of copies hits the market at once. If you want to understand market timing, start with pack cards. The earned pile decays too, faster and harder, and the contrast is one of the most useful things here. I'll get to it.

Two more ground rules. The numbers cover Diamonds and Red Diamonds, because from July on nearly all the top content shipped as Red Diamonds. And I leave out cards that launched already at their quick-sell price. Those can barely fall, and counting them was one of my biggest mistakes in July.

Exhibit A: Garrett Crochet

The 94 Vintage Crochet hit packs on May 29 at about 50,400 stubs. That was his ceiling. Watch what happened next:

• Day 7: 44,000
• Day 14: 33,600
• Day 21: 25,750
• Day 45: 13,849
• Low: 5,677 on September 9
• October 10: 7,751

That's 85% gone. He wasn't alone. The whole Vintage series dropped the same day, and every big-money pack card in it fell. Josh Bell, Terry Pendleton, Xander Bogaerts, Gary Sánchez and Chase Utley lost 34 to 66% in three weeks, and by October the ten priced well above quick-sell, Derek Jeter's 96 Red Diamond included, were all down 46 to 87%. The only two Vintage diamonds worth more on October 10 than at launch, Fred McGriff and Luis Castillo, were rewards, not pack cards.

Crochet from launch to October 10. Most of the fall came in the first six weeks. Since September he's sat just above his quick-sell price.

Crochet isn't weird. He's the shape of the whole pack market.

The half-life is real, and I can draw it

Every pack Diamond has a decay curve. I lined up the 178 that launched during the season above their quick-sell price and tracked what the typical one was worth as the days ticked by, as a share of its launch price:

The typical pack diamond, as a share of its launch-day price. Most of the fall is in the first two weeks. After that it mostly sits.

Down about 26% by the end of week one. Down about 40% by two weeks. It crosses half its launch price on day 42, and three months in it's still sitting right around half. That's the typical card: half do worse, and the chase cards do a lot worse. "Half-life" isn't a metaphor I reached for. It's what the data does.

The shape matters more than the end point. In July I called this a steady erosion. It isn't: it's a cliff and then a plateau. If you're going to sell a pack diamond for its price, the first two weeks are where the money goes.

Here's how I read what drives it. This is my explanation, not something the price data proves:

1. Supply accumulates. Every day, more copies get pulled and listed. Pack supply never shrinks.
2. Demand shrinks. Most of the people who wanted the card and could afford it bought it in the first few days. After that you're selling to a smaller and smaller pool.
3. Competition arrives. SDS drops new content every week, and every drop introduces cards fighting for the same lineup slots.

Of the pack diamonds that launched by the end of June, only 5% were back at their launch price on October 10. The typical one was at 45%.

Pulled or earned? The crater is a different shape

Here's the payoff for splitting the piles. Cards you grind out, from programs, XP paths and collections, decay on a different clock. The crater is front-loaded: most of the fall happens in the first few days.

Same season, two paths. Earned cards lose about a quarter of their price on day one and stay mostly below pack cards from there.

A pulled diamond is down about 26% after a week. An earned one is down 36%, and most of that happens on day one: the typical earned diamond is worth 74% of its launch price the day after it arrives. By day 45, earned cards are down 58% and pack cards 48%.

Remember Corbin Burnes? The 94 Breakout was an XP-path card. He launched at 450,000, was down to about 125,000 the next day, and was worth about 5,400 three weeks later. That's a 99% wipeout, and it had nothing to do with packs. Bryce Harper's 94 2nd Half Heroes did the same thing: 185,000 to under 7,000 in three weeks, −96%. Of the 15 worst three-week drops in my data, all 15 are earned cards.

But here's the part the July version got wrong. Earned cards that crater sometimes come back. Burnes sat around 5,000 through June and early July and was at 13,957 on October 10, nearly three times his low. Harper went from 5,299 to 29,580. Of the earned diamonds that launched by the end of June, a quarter were worth more on October 10 than on launch day, against 5% of pack cards. My guess is that once a program closes, no new copies arrive, and the market slowly soaks up the ones that are left. I haven't proved that. It's a slow bet, not a bounce, and it doesn't change the first-week rule.

So the rule bends depending on what you're holding. With a pack card you've got a few days to read the room. With an earned card, if you're not out by day two, you're already late.

The peak usually comes early

If the decay curve is the "what," peak timing is the "when." I checked, for every pack diamond with at least a month of prices, the day it hit its highest price:

When pack diamonds hit their highest price. Most peak in week one. About a third peak two weeks or more later.

39% peak on launch day, and 59% inside the first week. That's a smaller majority than I claimed in July, when I said 85%. The other big group, about a third, peaks two weeks or more after launch. I said in July that those were almost all upgrade cards. They aren't. The biggest groups are New Threads, Awards, Egg Hunt and World Baseball Classic. I don't have a clean reason why yet, so I'm not going to make one up.

What it means for you: the odds still favor selling early, but they aren't the sure thing I made them sound in July.

The four moments to sell

If you only think about selling at four moments, you'll do better than selling on a whim.

Moment 1 — Launch day, first 24 hours

If you pulled the card, you have about a day before supply catches demand. On day one the typical pack diamond is already down 8%, and about 7 in 10 are below their launch price. By day 7 it's about 8 in 10. Selling here gets you closest to the ceiling.

The exception is a card the market hasn't priced yet: a sleeper quirk combo, or a position-scarcity card that takes a few days to be recognized. Those can rise before they decay. Telling which is which means reading the card, not the price.

Moment 2 — Inside the first two weeks

Miss the launch-day window and the next-best exit is inside the first two weeks, before the curve flattens out. Don't wait for a streak of red days to tell you. As you'll see below, a streak doesn't tell you much. Check the Signal on the market table instead.

Moment 3 — Around a Roster Update

In July I said cards about to be upgraded run up 99% in the three days before an update. I can't reproduce that number, and it was wrong. Across all 26 updates this season, cards that got upgraded rose about 4% in the three days before. Cards that didn't get upgraded didn't move. On cards worth 5,000 stubs or more they slipped about 1%.

So there's no rush to dump a card that isn't on anyone's upgrade list. And for a card that might get boosted, the move is the opposite of selling early. I tested that in Buy a Week Out. Don't Sell the Night Before.: the money is in the upgrade itself, and you only get it by still owning the card.

Moment 4 — End-of-cycle clearance

Every content cycle ends. Series sunset, themed packs leave, Live Series cards get power-crept. If you've held a pack diamond more than a month and it isn't a card you actually play with, sell it. This isn't about hitting a peak. It's about not dragging dead inventory into the next cycle.

The signals to watch (and the one everybody gets wrong)

Four signals, all on the market table:

The market table, signed in, in July. The Signal column reads Buy / Wait / Overpriced, in the same row as the 24h sparkline. The sparkline and Buy Now floor are free; Signal and Value Gap are Pro.

• The 24-hour sparkline (free). Your fastest read on direction.
• The Buy Now floor (free). If it's at or near an all-time low for the card, the market has decided. Don't fight it.
• The Value Gap (Pro). Flags cards the market is overpaying for upgrade potential. Own one that's gone negative and you're holding a known-overpriced position.
• The Signal (Pro): Buy / Wait / Overpriced. A card is "Overpriced" when it's trading 15%+ above its own 7-day average, and "Buy" when it's 10%+ below.

Now, the thing everybody gets wrong. The folk wisdom is "two red days in a row means sell, five red days means you already should have." It sounds right. It isn't, but it isn't backwards either, which is what I said in July.

Chance a pack diamond is cheaper three days later. A run of down days barely changes the odds.

On a pack diamond trading above its quick-sell price, two red days leave it lower three days later 47% of the time, against 55% on any random day. That's a slight edge for holding, not a bounce: it's a coin flip. A longer slide doesn't add anything, and five or more red days is no better than any other day. On cards worth 25,000 stubs or more, the season-long slide wins anyway: after two red days, 60% of them are lower a week later.

My July version said two red days made a card much less likely to keep falling, and that it "tends to bounce." Part of that came from counting cards sitting at their quick-sell price, which rarely close lower, so their flat days looked like non-falls. Take those out and the gap shrinks to 55% against 47%: a small edge, not a bounce.

The streak isn't the signal. The Signal is. It measures the card against its own 7-day average, not against yesterday. A card that's "Overpriced" is the one to lighten up on, whatever color the last two candles were.

When NOT to sell

The shorter list, on purpose:

• Cards you actively play. Performance beats profit. If the card wins you games, the stubs you'd recover don't.
• Cards on a credible upgrade path. See Moment 3. Holding through the update is where the upgrade money is.
• Cards at the quick-sell price. If quick-selling pays as much as the market does, there's nothing left to time. The market gave up before you did.

What flash sales do to all of this

There's one more event worth knowing about: the flash sale. SDS puts selected packs on sale in the Show Shop for a few hours, sometimes several times in one day. I looked at three flash-sale days SDS announced.

In July I said the April 21 flash sale knocked the diamond market down 25% in one day. That number most likely measured something fragile: the middle price across every diamond listed that day. Prices are spread thin around the middle, so that one figure can swing much further than the typical card does. Measured card by card, the typical diamond was 12% lower than the day before on April 21, 5% lower on May 13 and 8% lower on May 26. I only have whole-day prices for those dates, so I can't show the sale caused the drop, just that it happened on sale days. And dips that size aren't unique to these three days: the typical diamond fell 5% or more on 18 of the 207 days I have:

The typical Diamond around three flash sales. Two bounced the next day. May 26 didn't.

April 21 and May 13 were back near even the next day. May 26 wasn't: two days later the typical diamond was still about 7% below where it started. (The day after that was the Vintage launch and a roster update, so I won't read anything into day three.) In July I said every flash sale had the same fingerprint, a sharp dip and a fast recovery. Two out of three did.

So the play is smaller than I made it sound. Don't panic-sell on a flash-sale day, because the dip is usually modest and often bounces. And if you've been eyeing a card, a flash-sale afternoon is a decent time to buy, not a fire sale.

What this all means

Most people sell a diamond for one of three reasons: they need stubs and grab whatever they can stand to lose; they notice it decayed and panic-sell at the floor; or they never sell, and quick-sell it later for a fraction of what they paid. All three are the wrong move.

The right move is to plan the sell on the buy day. Decide your window before you own the card. For a pack diamond, that window is the first two weeks. Treat every Diamond like a fixed-period position, because that's what the data says it is.

You won't nail every sell. Nobody does. The point isn't precision. It's not being the person still holding the card at end-of-cycle because they never decided when they were getting out.

Where to go next

The buying side is the mirror image: the best time to buy a pack diamond is after the cliff, once it's sitting on the plateau. For which hour to click, The Market Sleeps When You Do has the hourly data. If you'd rather not time every position by hand, the Diamond Radar flags the cards most likely to be upgraded at the next roster update, and OpScore tells you which cards are worth holding for reasons that have nothing to do with price.

Every number here comes from DiamondOps market data: 468,197 daily price records for every card on the market, March 17 to October 10, 2026. "Price" is the day's average Buy Now listing, not a sale. The decay and signal numbers cover pack Diamonds and Red Diamonds trading above their quick-sell price. Drafted and crunched with editorial AI on my data; the takes, and the July mistakes, are mine.

I'm Shaun. If something is wrong, tell me.