20% of coins mined in first 4 years, 0% thereafter:

"At first, 50 ZEC will be created every ten minutes. 80% of the newly created ZEC will go to the miners, and 20% ZEC to the founders.

Every four years, the rate of ZEC being created will halve (again, just like in Bitcoin). After the first four years the ZEC created per ten minutes will drop to 25ⓩ, but after the first four years, 100% of it goes to the miners."

https://z.cash/blog/funding.html

"At first, 50 ZEC will be created every ten minutes. 80% of the newly created ZEC will go to the miners, and 20% ZEC to the founders.

Every four years, the rate of ZEC being created will halve (again, just like in Bitcoin). After the first four years the ZEC created per ten minutes will drop to 25ⓩ, but after the first four years, 100% of it goes to the miners."

https://z.cash/blog/founders-reward-transfers.html

Too late to edit and I wanted to quote the second link correctly:

"The 10% of the total supply that makes up the Founders' Reward is distributed between launch and the first halving (at block 850,000). During this period (which will last approximately four years), half of the total monetary base will be generated. After the first halving, there will be no more Founders' Reward, and all newly-created ⓩ will be received by miners."

https://z.cash/blog/founders-reward-transfers.html

I make no judgment on whether this is good, or bad, or other, just wanted to present the source's position on the matter.

They are taking 20% during the most important period of distribution. That is worse than any kind of premine. All Zerocoin based coins had the same ridiculous rewards and all dead yet or barely breathing.

No; it's 20% of the first half, the distribution of the first four years...

Which amounts to 10% of the total coins that will be ever possible to create.