GoodAvatar credits are valid for 180 days from the date they are added to your account. That applies to both the 100 welcome credits and purchased packs.
The clock starts when the credits land in your balance, not when you create the video task. If you buy a pack for a launch and use part of it, the remaining credits keep the same expiry date as the original purchase.
A prepaid balance is useful when it matches a real production window. Six months is long enough to cover a launch, a campaign, or a batch of course modules, and short enough that the balance does not turn into an indefinite liability.
GoodAvatar is still pay-as-you-go: there is no monthly subscription, no seat fee, and no automatic renewal. The difference is that the balance has a defined life.
A 30-second video costs 150 credits, so the Starter pack covers five 30-second clips. That is usually enough to judge whether the workflow fits before committing to a larger pack.
If you need the no-subscription framing first, read GoodAvatar without a subscription. For the per-clip cost, use the cost calculator.
Use the 100 welcome credits for one 20-second clip. Create a video, check the result, and buy a pack only when you know the workflow fits your production.