As a general rule, the smaller your channel is, the shorter the steps are between each milestone you get. As your channel grows, the gaps between milestones are bigger.
Also, milestone steps vary by type. Getting 5 new views is significantly easier than uploading 5 whole videos so the steps between upload milestones and views milestones are different.
To take one example below under Subscribers it says "(550-1,000) every 50". This means that once you reach 550 subscribers, you will earn a new milestone every 50 new subscribers you get until you reach 1,000. That means certificates at 550, 600, 650, 700, 750, 800, 850, 900, 950, 1,000.
Subscribers
(1-10) every 1
(15-100) every 5
(110-250) every 10
(275-500) every 25
(550-1,000) every 50
(1,100-2,500) every 100
(3,000-10,000) every 500
(11,000-100,000) every 1,000
(102,500-250,000) every 2,500
(260,000-10,00,000) every 10,000
(1,010,000-10,000,000) every 50,000
(10,500,000-50,000,000) every 500,0000
(60,000,000+) every 1,000,000
Video Views
(1-100) every 10
(150-500) every 50
(600-1,000) every 100
(1,500-5,000) every 500
(6,000-10,000) every 1,000
(15,000-100,000) every 5,000
(125,000-500,000) every 25,000
(600,000-1,000,000) every 100,000
(1,500,000-10,000,000) every 500,000
(20,000,000-50,000,000) every 1,000,000
(60,000,000-1,000,000,000) every 10,000,000
(1,050,000,000+) every 50,000,000
Uploads
(1-30) every 5
(40-100) every 10
(125-250) every 25
(300+) every 50