INSP vs. VIIIX

Last updated Jul 14, 2026

INSP (Inspire Medical Systems, Inc.) is a stock, while VIIIX (Vanguard Institutional Index Fund Institutional Plus Shares) is S&P 500 fund tracking the S&P 500 Index. Over the past 5 years, INSP returned -21.80%/yr vs 13.38%/yr for VIIIX. At a 0.42 correlation, their price movements are largely independent.

Performance

INSP vs. VIIIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Inspire Medical Systems, Inc. (INSP) and Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, INSP achieves a -44.31% return, which is significantly lower than VIIIX's 11.34% return.

INSP

• 1D: -0.77%
• 1M: 20.28%
• 6M: -47.01%
• YTD: -44.31%
• 1Y: -60.57%
• 3Y*: -46.00%
• 5Y*: -21.80%
• 10Y*: —

VIIIX

• 1D: 0.43%
• 1M: 2.02%
• 6M: 9.19%
• YTD: 11.34%
• 1Y: 22.45%
• 3Y*: 21.51%
• 5Y*: 13.38%
• 10Y*: 15.39%

*Multi-year figures are annualized to reflect compound growth (CAGR)

INSP vs. VIIIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018
INSP Inspire Medical Systems, Inc.	-44.31%	-50.25%	-8.87%	-19.24%	9.48%	22.31%	153.46%	75.64%	72.52%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	11.34%	17.87%	26.29%	25.79%	-18.14%	28.69%	18.41%	31.48%	-3.59%

Correlation

The correlation between INSP and VIIIX is 0.21, which is low. Their price movements are largely independent, making them effective diversification partners.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.21
Correlation (3Y) Calculated over the trailing 3-year period	0.31
Correlation (5Y) Calculated over the trailing 5-year period	0.41
Correlation (All Time) Calculated using the full available price history since May 3, 2018	0.42

Over the past year, the correlation between INSP and VIIIX has dropped to 0.21 - well below their long-term average of 0.42, suggesting their price drivers have been diverging.

Return for Risk

INSP vs. VIIIX — Risk / Return Rank

Compare risk-adjusted metric ranks to identify better-performing investments over the past 12 months.

INSP

INSP Risk / Return Rank: 11
INSP Sharpe Ratio Rank: 10
INSP Sortino Ratio Rank: 11
INSP Omega Ratio Rank: 9
INSP Calmar Ratio Rank: 10
INSP Martin Ratio Rank: 15

VIIIX

VIIIX Risk / Return Rank: 65
VIIIX Sharpe Ratio Rank: 64
VIIIX Sortino Ratio Rank: 59
VIIIX Omega Ratio Rank: 61
VIIIX Calmar Ratio Rank: 66
VIIIX Martin Ratio Rank: 77

The rank (0–100) shows how this investment's returns compare to the risk taken. Higher = better. Based on the past 12 months of data, combining Sharpe, Sortino, and other metrics used by quantitative funds and institutional investors.

INSP vs. VIIIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Inspire Medical Systems, Inc. (INSP) and Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX). Risk-adjusted metrics are performance indicators that assess an investment's returns in relation to its risk, enabling a more accurate comparison of different investment options.

Values are calculated on a 1-year rolling basis and updated daily. Risk-adjusted metrics are more stable over longer periods — use the period switch above to explore them.

	INSP	VIIIX	Difference
Sharpe ratio: Return per unit of total volatility	-0.81	1.77	-2.58
Sortino ratio: Return per unit of downside risk	-1.13	2.43	-3.56
Omega ratio: Gain probability vs. loss probability	0.84	1.32	-0.48
Calmar ratio: Return relative to maximum drawdown	-0.84	2.49	-3.33
Martin ratio: Return relative to average drawdown	-1.24	10.93	-12.17

INSP vs. VIIIX - Sharpe Ratio Comparison

The current INSP Sharpe Ratio is -0.81, which is lower than the VIIIX Sharpe Ratio of 1.77. The chart below compares the historical Sharpe Ratios of INSP and VIIIX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Drawdowns

INSP vs. VIIIX - Drawdown Comparison

The maximum INSP drawdown since its inception was -87.72%, which is greater than VIIIX's maximum drawdown of -55.18%. Use the drawdown chart below to compare losses from any high point for INSP and VIIIX.

Drawdown Indicators

	INSP	VIIIX	Difference
Max Drawdown Largest peak-to-trough decline	-87.72%	-55.18%	-32.54%
Max Drawdown (1Y) Largest decline over 1 year	-72.19%	-8.90%	-63.29%
Max Drawdown (3Y) Largest decline over 3 years	-87.72%	-18.75%	-68.97%
Max Drawdown (5Y) Largest decline over 5 years	-87.72%	-24.50%	-63.22%
Max Drawdown (10Y) Largest decline over 10 years	—	-33.79%	—
Current Drawdown Current decline from peak	-84.25%	-0.32%	-83.93%
Average Drawdown Average peak-to-trough decline	-28.31%	-9.99%	-18.32%
Ulcer Index Depth and duration of drawdowns from previous peaks	49.00%	2.02%	+46.98%

Volatility

INSP vs. VIIIX - Volatility Comparison

Inspire Medical Systems, Inc. (INSP) has a higher volatility of 11.53% compared to Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX) at 4.26%. This indicates that INSP's price experiences larger fluctuations and is considered to be riskier than VIIIX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	INSP	VIIIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	11.53%	4.26%	+7.27%
Volatility (6M) Calculated over the trailing 6-month period	42.88%	9.96%	+32.92%
Volatility (1Y) Calculated over the trailing 1-year period	75.08%	12.52%	+62.56%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	60.33%	16.99%	+43.34%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	60.38%	18.04%	+42.34%

Dividends

INSP vs. VIIIX - Dividend Comparison

INSP has not paid dividends to shareholders, while VIIIX's dividend yield for the trailing twelve months is around 2.47%.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
INSP Inspire Medical Systems, Inc.	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	2.47%	2.11%	3.66%	2.66%	3.39%	4.79%	3.07%	2.86%	2.45%	1.84%	2.38%	2.47%

Frequently Asked Questions

Can I hold both INSP and VIIIX in my portfolio?

INSP and VIIIX have a correlation of 0.21, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, INSP or VIIIX?

INSP has higher volatility (11.53%) compared to VIIIX (4.26%). In terms of maximum drawdown, INSP dropped -87.72% vs VIIIX's -55.18%.

Which has better risk-adjusted returns?

VIIIX currently has the higher Sharpe Ratio (1.77 vs -0.81), meaning it's delivered slightly more return per unit of risk over the trailing 12 months. However, this ranking shifts over time - use the Risk/Return Score above for a more comprehensive view that combines Sharpe, Sortino, and other measures used by quantitative funds.