The first [whatever increment] will always be the hardest. Exponential growth looks the same on any scale.
While this is true of pure exponential growth, you have to consider contributions as well. Assuming mostly constant contributions your first <smaller increment> will be easier than your first <larger increment>. This makes sense. If you're saving $10k per year then your first $10k will be accomplished in just under a year with almost no help from compounded growth.
At $10k saved per year compounded at 7%:
- $10k saved takes 12 months
- $20k saved takes 23 months
- $100k saved takes 91 months
- $200k saved takes 150 months
- $1 million takes 357 months
- $2 million takes 465 months
Therefore (with these assumptions), the first $10k is almost as easy as the second $10k. The first $100k is 54% harder than the second $100k. And the first $1 million is more than three times as hard as the second $1 million.
Obviously these numbers shift with different assumptions, but the first <larger increment> will always be relatively harder compared to the second <larger increment> than with a <smaller increment>.
