MDM, is there a way to look at the weighted average of the underlying fund ratios? I'm not clear on where to look for that.

You would have to find the expense ratios of the underlying funds, then multiply each by the fraction of the target date fund devoted to the underlying fund.

For example, VTTSX holds

1. Vanguard Total Stock Market Index Fund Investor Shares 54.10%

2. Vanguard Total International Stock Index Fund Investor Shares 35.90%

3. Vanguard Total Bond Market II Index Fund Investor Shares† 7.10%

4. Vanguard Total International Bond Index Fund Investor Shares 2.90%

The expense ratios of those funds (or a close approximation) are

1. 0.14%

2. 0.17%

3. 0.09%

4. 0.13%

The weighted average is .541 * 0.14% + .359 * 0.17% + .071 * 0.09% + .029 * 0.113% = 0.15%, the same as VTTSX's expense ratio.