Net margin debt is a measure of leverage investors carry in their markets exposures, or, put differently, the level of debt accumulated on margin accounts. Back at the end of March 2018, the level of margin debt in the U.S. stock markets stood at just under $645.2 billion, second highest on record after January 2018 when the total margin debt hit an all-time-high of $665.7 billion, prompting FINRA to issue a warning about the unsustainable levels of debt held by investors.
Here are the levels of gross margin debt:
And here is the net margin debt as a ratio to the markets valuation - a more direct measure of leverage, via Goldman Sachs research note:
Which is even more telling than the absolute gross levels of margin debt in the previous chart.
Per latest FINRA statistics (http://www.finra.org/investors/margin-statistics), as of the end of April 2018, debit balances in margin accounts rose to $652.3 billion, beating March levels
And things are even worse when we add leveraged ETFs to the total margin debt:
In simple terms, we are at systemic levels of risk relating to leverage in the equity markets.