Just Work Backwards To Get Insight

Let’s use the 2035 Target Date Fund. It is -4.44% as of 2/8/2022.
The S&P 500 is -5.82%. Two bond indices are approximately -1.8%.
So you have

100% * -4.4% = (Stocks allocation % * -5.82%) + (Bonds allocation % * -1.80%). Let’s assume that cash is zero (which can be invalid, but the illustration here still works.

You can find the solution here.
Stocks allocation % = 65%
Bonds allocation % = 35%

It’s just another way of looking under the hood, so that you can have an idea how your Targeted Retirement Fund is created. Notably you can now understand the returns of the past 12-months as shown in the table. These Targeted Retirement Funds reflect the professional output of a diversified portfolio, adjusted for end dates. Note that all of these figures are much much different than the overall index, the top row, of 23%.