Net worth includes more then just savings though. Using their example of a 30 year old making 50K. I assume you are making 50K six years out of school and you started out a $30K a year with $5K increases after a couple years to get you quickly to that $50K in six years. More likely you were making scenario would be making 43.5k at age 25 with 3% cost of living increases. But make the assumption you start out at $30k for now.
I also made the assumption of an 8% return–likely this would be higher for a 30 year old as they can afford to be more aggressive in the market. But a 8% return is not unreasonable over the long term in my experience.
So assume you made the following:
age 25—$30,000—$3000 saved and return of .08 = $3240
age 26—$30,000—$3000 saved and return of .08 = $3240+3000 x.08=$6739
age 27—$35,000—$3500 saved and return of .08 = $6739+3500 x.08=$11,058
age 28—$40,000—$4000 saved and return of .08 = $11058+4000 x.08=$16,262
age 29—$45,000—$4500 saved and return of .08 = $16262+4500 x.08=$22,424
age 30—$50,000—$5000 saved and return of .08 = $22424+5000 x.08=$29,618
So at age 30 you have $30K plus you have a house (hopefully) which has some equity in it–so lets say you bought it for $100K and it is now worth $110K and you still owe $90K on it, thus you have $20K equity. You own a car which has a value which is part of your net worth. Money in your checking and savings is part of your net worth, etc.
So just with the $30K you have saved and the $20K in your house you have $50K net worth. If I used the starting salary of $43.5K in my sample above I get this person having $36,395 at age 30. So the value of the rest of the assets only needs to be $14K to get to the magical $50k. And there is nothing magical about the 10%, you can save even more then that. It all depends on how frugal you choose to be. You can put away $5K in an IRA and 15% of your pretax earnings in a 401k – so our 30 year old can save $12500 each year (if he can do it!).
Also remember–it is a ‘rule of thumb’ and any individual won’t fit into it. But it is is I believe solidly based by using the power of compounding and actually putting away large amounts (i.e 15% of your gross pay) away. I do that now-wish I had earlier! But even with that, I am very far ahead of the net worth in that chart for my age group, but both my wife and I save a large amount of our income every year for retirement.
ps-hope I didn’t make any math errors above as I did it pretty quickly!