Price & Market BehaviorExtended setexperimental liveNew

Borrow Rate Spike Short

Updated dailyData needs: lowshort only

2008

Boehmer, E., Jones, C.M., Zhang, X. (2008). "Which Shorts Are Informed?" Journal of Finance, 63(2), 491-527. Combined with Drechsler-Drechsler 2014 NBER.

Read the paper →

In plain terms

When the cost to short a stock jumps sharply over a month (top 10% of normal moves), informed shorts are paying a premium to get in. Short the stock for 4-8 weeks.

How it works

A sharp INCREASE in borrow fee, independent of absolute level, means short demand is overwhelming supply — informed shorts are willing to pay up to get in. The 30-day delta of borrow rate, ranked top decile against trailing-year own distribution, captures the demand-acceleration signal.

Live results

9 times picked on its own · 28 times inside a blend (27 beat the stock) · updated 2026-06-06

This strategy is a frequent ingredient in blends that combine a few strategies on one stock. It has contributed to 28 such blended picks (27 of which beat simply holding the stock). Picking it on its own is only one of the ways it shows up.

How its picks scored vs. buy & hold

Each pick is graded on a recent year it was never tuned on, against simply owning the same stock

Where its edge concentrates

Share of picks in each company-size group that beat buy & hold

How often it trades

Active vs. patient. Bars on the left mean it waits for rare setups; bars on the right mean it trades often

Return vs. buy & hold

How much each pick beat or trailed simply owning the stock over the test year (extreme microcap moves trimmed)

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Data dependencies

Daily prices
Adjusted-close OHLCV for every US-listed ticker; primary price feed.
Stock borrow rates
Daily borrow-fee curve from prime-broker feeds.

Expected edge

Reported return: -1 to -2% over 20-40d
Tested over: T+1 to T+40d

~-1 to -2% over 20-40d post-spike (BJZ 2008 informed-short result).

Example tickers where this is likely to fire

GME TSLA MARA RIOT

Illustrative only, the signal fires based on the live data, not a fixed list.

Related families

Borrow Rate SpikePrice & Market Behavior

When the cost to borrow a stock spikes, shorts are paying premium to bet against it — usually a bearish signal, except at extremes where they get squeezed.

Borrow Rate Level ShortPrice & Market Behavior

When the cost to short a stock annualizes above 10% (hard-to-borrow), the stock tends to underperform by roughly 3-4% per month. Short these expensive-to-borrow names for the next 4-12 weeks.

Short Interest ChangePrice & Market Behavior

Watches FINRA's daily short-sale volume z-score. Aggressive new shorting in a falling tape = continuation; extreme highs that revert = squeeze fade.

Explore Borrow Rate Spike Short on alphactor.ai

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