I just calculated this today in case to run numbers in case I want to semi-retire and just work enough to cover expenses until my portfolio hits the magic number for full retirement. It is a liberating feeling to know that these few years I have been contributing should already be enough to give me a very comfortable retirement at traditional retirement age.
For my calculations, I figured out what my portfolio should look like every year based on my current contributions, then figured out at what age that resulting portfolio would hit $1 million without any further contributions.
Since we've only been investing about 2 years, it would take until age 62 for us to hit $1 million without any further contributions (assuming 7% growth). But if we invest one more year at our current rates, that portfolio will hit $1 million at age 57.
These were my results (number is projected portfolio in X years):
current: 92k, 1 million at 62
1 year: $139k, 1 mil at 57
2 years: 198k, 1 mil at 53
3 years: 260k, 1 mil at 50.5
4 years: 328k, 1 mil at 48
5 years: 400k, 1 mil at 46
6 years: 477k, 1 mil at 44.5
7 years: 560k, 1 mil at 43.5
8 years: 649k, 1 mil at 42
9 years: 744k, 1 mil at 41
10 years: 847k, 1 mil at 40.5
11 years: 957k, 1 mil at 39.5
Now to go plug away at a few side hustles and trim the years down even more.