Inbreeding in Dragonbred is one number, F, that measures how closely a pair is related over the last six generations. Every bit of F costs you something you can count: fewer eggs, more eggs that never develop, and a lower hatch chance for the ones that do. Pair a brother and sister and the clutch is 25% inbred, which means one egg fewer and a 30% chance that each remaining egg does not develop.
That price is sometimes worth paying. Line-breeding is how keepers fix a recessive when only one family carries it. The trick is knowing exactly what you are spending and when to stop.
What the F number actually measures
Dragonbred uses Wright's coefficient of inbreeding. In plain terms, F is the chance that the two copies of a gene in a baby both trace back to the same ancestor. The game walks the pedigree six generations up from each parent, finds every ancestor they share, and adds up the paths. A shared ancestor seven or more generations back does not count.
Crate dragons have no recorded parents, so each one starts at 0% and is unrelated to everything else in your pen. That makes them your clean outcross stock.
Here is what the common pairings come to:
| Pairing | F of the babies |
|---|---|
| Unrelated | 0% |
| First cousins | 6.25% |
| Half brother and sister | 12.5% |
| Full brother and sister | 25% |
| Father and daughter, or mother and son | 25% |
| Two babies of a brother and sister pairing | 37.5% |
| One more generation of the same | 50% |
The numbers climb fast when you keep going back to the same family, because the ancestors' own inbreeding is counted too.
F on a card is not the generation
This trips up a lot of new keepers. A dragon card shows its generation as "F" plus a number, so a grandchild of crate dragons reads F2. That is only how many generations it sits below dragons with no recorded parents. Generation is the higher of the two parents' generations, plus one. Inbreeding is shown separately, as a percentage labeled Inbreeding. A dragon can be F10 and 0% inbred, and there is an achievement for exactly that.
What inbreeding costs a clutch
The cost comes in four parts. The first three depend on how related the pair is. The last depends on how inbred the parents already are.
- Fewer eggs. The pairing loses 4 × F eggs. Full siblings lose one egg; half siblings lose about half an egg on average.
- Eggs that do not develop. Each egg fails with a chance of 1.2 × F. On the hatch screen these read "Did not develop".
- A lower hatch chance. For the eggs that do develop, the incubator's hatch chance is multiplied by (1 − 0.8 × F).
- Inbred parents. A dam who is herself inbred lays smaller clutches, by up to 25% × her own F. And each egg is infertile with a chance of 0.35 × the average of both parents' own F, up to a ceiling of 90%.
Put the first three together for the usual pairings:
| Pairing | F | Eggs lost | Won't develop | Hatch chance cut |
|---|---|---|---|---|
| First cousins | 6.25% | 0.25 | 7.5% | 5% |
| Half siblings | 12.5% | 0.5 | 15% | 10% |
| Full siblings | 25% | 1 | 30% | 20% |
| Two babies of full siblings | 37.5% | 1.5 | 45% | 30% |
A worked example
Say your dam lays an average clutch of four and your incubator is well upgraded, so nearly every healthy egg hatches. Unrelated, you expect close to four hatchlings.
Now pair full siblings. Four eggs drop to three. Each of those has a 30% chance of not developing, leaving about 2.1. The hatch chance is then cut by a fifth. You end up with roughly 1.6 to 1.7 hatchlings on average, well under half of what an unrelated pair gives you. The morph odds per hatchling are the same; there are just fewer hatchlings to roll them.
Why the second generation hurts more
The real damage comes when inbred dragons are paired with each other. Their babies are 25% inbred already, so pairing two of them stacks the penalties.
The pairing itself is 37.5%: 1.5 eggs lost, 45% that won't develop, a 30% cut to the hatch chance. On top of that, the dam's own 25% shrinks her clutch by about 6%, and each egg has an 8.75% chance of being infertile because both parents carry 25%. One more generation of the same and the pairing hits 50%.
Reading the warnings on the Breed tab
You never have to work this out by hand. When you place a related pair, the Breed tab names the relation ("Related: these two are brother and sister") and tells you how inbred the babies will be. The game recognizes parents and children, grandparents, siblings, half siblings, aunts and uncles, cousins, and more distant relatives.
Below that, the inbreeding panel gives the F value, a label, and the cost to this clutch in eggs, eggs that won't develop, and hatch chance. The breeding slip on the right includes the infertility chance. The labels run like this:
| Label | F |
|---|---|
| Unrelated | 0% |
| Distant | under 5% |
| Line-bred | 5% to under 20% |
| Inbred | 20% to under 40% |
| Heavily inbred | 40% and up |
A dragon's own page shows its Inbreeding percentage and what that will cost it as a parent, so check it before you pick a dam.
When a related pairing is worth it
Recessive genes are the usual reason to pair relatives. Say the only Striped carrier in your pen is one proven het female. Pair her with any unrelated male and each baby is 50% het Striped, but none can show it. To make a visual Striped you need two carriers, and if her family holds the only copies in your pen, you either pair inside it or wait for a carrier from somewhere else.
The quickest inside route is a son back to his mother. She is a proven het; he is 50% het, so each egg has about a 12.5% chance of being Striped, at a cost of 25% F. Two of her babies paired together are also 25% F but only about 6% Striped per egg, because neither one is proven. The odds cards on the Breed tab will show you these numbers before you commit.
Once you have the visual, get out of the family:
- Pair the visual with an unrelated dragon. Every baby is a 100% het, and the clutch is 0% inbred.
- Prefer half siblings or cousins to full siblings when you must stay in the family; 12.5% and 6.25% cost a fraction of what 25% does.
- Use crate dragons as outcrosses. They arrive unrelated to everything and often carry possible hets of their own.
- Never pair two inbred dragons with each other if there is any other option.
Building a clean line
The achievement A clean line asks for a generation 10 dragon with 0% inbreeding. You only get there by planning an unrelated partner at every step, which is good practice anyway. Keep a few unrelated families going side by side and cross them, rather than pushing one family deeper. The breeding project guide walks through laying out unrelated lines for exactly this.
If you want to see how a pairing scores before you spend a clutch on it, the Breed tab in Dragonbred shows the F value the moment both parents are in place.
Frequently asked questions
What is a safe inbreeding percentage in Dragonbred?
Under 5% the Breed tab calls a pairing Distant, and the costs are small: at 5% you lose a fifth of an egg on average and 6% of eggs fail to develop. Above 20% the game labels it Inbred and the losses get serious.
Does inbreeding change the morph odds?
No. The chance of each look per hatchling comes from the genes, as in dragon genetics 101. Inbreeding changes how many eggs are laid, develop, and hatch.
Is the F on a dragon card its inbreeding?
No. "F" followed by a number, like F3, is the generation. Inbreeding is shown as a separate percentage on the card and on the dragon's page.
How far back does Dragonbred check for relatives?
Six generations. A common ancestor further back than that does not add to F.
Published October 6, 2026 · updated October 22, 2026
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