The DOE’s struggling charity lost a staggering $660,000-plus selling securities during a bull market — a move officials said Monday was intended to create a “lower-risk portfolio.”

The Fund for Public Schools realized $20.4 million by unloading unspecified financial assets between July 1, 2016, and June 30, 2017, according to its most recent IRS filing.

But initial purchase costs and sales expenses totaled $21.1 million, resulting in a net loss that exceeded the $583,280 in investment income the non-profit organization reported for fiscal 2016 — and put its total revenues in the red by $76,828.

By contrast, most investors were raking in profits during the same period, when the three major US stock market indices rose between 15 and 26 percent.

The fund’s investment loss came amid a steady plunge in donations since Mayor de Blasio took office, with annual contributions falling from $31.4 million to just $15.4 million.

The Department of Education, whose chancellor chairs the fund, said the fiscal 2016 loss was“a result of a change in investment strategy from a higher-risk portfolio to a lower-risk portfolio” and didn’t involve any grant money or affect any programs.

It also said the fund made $566,452 in unrealized gains during the year.

Marcus Owens, former director of the IRS’s Exempt Organizations Dvision, called the loss “unusual, in the sense that it was a bull market.”

“It does suggest that perhaps better investment advice could be obtained,” said Owens, now a partner at the international law firm Loeb & Loeb.

The fund’s fiscal 2016 tax-exempt return also lists an unusual expense of $571,180 that’s identified only as “LOSS ON REGRANTED CONTR.”

The DOE said the notation was made to write off the unused portion of a multi-year, $5 million grant from the Bill and Melinda Gates Foundation to pay for a teacher-training program that came in under budget.