A few congress people put forth a bill that would add a 0.1% tax on trades. This would be a rounding error for most traders, but a significant value for HFT.

https://www.brookings.edu/opinions/congress-wants-to-tax-sto...

I wonder what happened to it.

Raising the financial transaction tax to 0.1%, 1$ per $1000 would eliminate the vast majority of unproductive and rent seeking HFT without negatively effecting liquidity. The US already has an FTT to fund the SEC, implementation should be straightforward. Currently the rate is very low, about 0.002%. Raising the rate would be minimally impactful for longer term investors and generate on the order of $50b a year for the government.

Hong Kong has an FTT of 0.13% currently, it was 0.1% from 1993-2021 so you can compare HFT impacts on these markets. Or compare dozens of other countries with similar rates, Switzerland, Taiwan, France, Italy, Japan.

If you buy a stock, you must keep (hold) it for eg. 30 days (or 7, or 60, or whatever).

Compute all you want, whenever you want, but instead of millisecond timings, optimize stuff for at least some time.

Maybe even a tax on stock profits, which is really high and falls after some time of ownership of such stock (we have this in slovenia, but it's not really high in the first place, and time brackets go less than 5 years (25%), 5-10 years (15%), 10-15 years (10%) , 15-20 years (5%), and zero tax after that.

> What would that look like?

One attempt is the exchange IEX [0] which introduced a ~350 microsecond delay to everything simply by running incoming order data through a ~60km loop of fiber-optic cable.

Perhaps not the most, er, featureful solution, but it's very easy to audit and argue that there are no biases or backdoors.

[0] https://en.wikipedia.org/wiki/IEX

What about a flat "Tobin tax" charged on each transaction so that it becomes very expensive to do lots of small trades quickly and encourages doing bigger trades at lower frequency?

https://en.m.wikipedia.org/wiki/Tobin_tax

The best solution I've seen is to do batch auctions every millisecond or so, and randomize matches within that window (for market orders or limit orders at the same price). You could use a longer window to include slower players in the market.

Limit trades to once per hour, then, and require a human to enter them.

Small cost per trade (tax/fee)

Minimum time between buying and selling the same ticker

Mandatory network 'speed bump' of a few ms between the exchange and any trading parties