On 3/6 I bought some shares of CXSE, which happened to be commission-free on that platform. By this morning it was up 4%+, but of course on a commission-free trade I would eat a penalty for short-term turnaround. So the question du jour is... how much money do you have to throw around for it to be worth the commission fees?
Fidelity's commission per trade is $4.95, plus .01 to .03 per $1000 on sell orders. ETrade and TD's commissions are $6.95 per trade, but their minimum balances are lower than Fidelity's. Even assuming maximum fees (.03 per 1000 or fraction thereof) on Fidelity sell orders, it remains cheaper than TD for trades up to about $133,000.
So let's say I'd bought $1000 worth of CXSE at 89.64/share, and let's pretend CXSE isn't in any of those 3 brokerages' commission-free ETF programs. And then let's say I sold those shares today around noon, at 93.10. That was a 3.86% gain, so I get 1038.60 back before commissions and Fidelity's sell-order jigger. After commissions, at Fidelity I spent 1004.95 and got back (1038.60-(4.95+.06)) = 1033.59, for a net ROI of (1033.59-1004.95) = 28.64. At ETrade or TD, the same flip cost 1006.95 up-front and returned (1038.60-6.95) = 1031.65, for a net ROI of (1031.65-1006.95) = 24.70. Depending on brokerage house, my 3.86% gain got whittled down to 2.86% or 2.47%. So at the $1000 purchase mark, commissions ate 26% to 36% of profit. Understanding costs as a percentage of return is critically important in deciding a meaningful buy-in level to flip stocks. For brevity's sake I'll call it cost-return ratio (CRR).
By doubling the gross purchase to $2000, CRR gets leveraged down to 13% (Fidelity) or 18% (Etrade/TD). At Fidelity's $2500 minimum "for some accounts", a 3% gain nets $65 ROI, and CRR stays around 13%. At my experience level (novice), it's probably not at all wise to gamble retirement funds in the market, so any gains are going to be taxed at regular short-term capital gains rates, i.e. same as employment income: ~12% federal (2018) and 5.75% state.
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Trading for serious income
Playing the market is a form of gambling. Unlike casino games, it's exceedingly rare to lose your whole wager on a given trade. An stock traded on major exchanges doesn't just collapse from, say, $20 per share to nothing. But it is easy spin your wheels, losing bites to commissions and taxes on the upside, and eating losses when overvalued dividend-poor stocks correct on the downside.
For perspective on what would make trading a serious income stream, consider your household budget. You rent a modest apartment, you split rent and utilities and groceries evenly with a spouse or partner, you have a modest financed vehicle. Altogether, your share of shared expenses and personal bills comes to $17,500. Assuming combined federal and state income tax rates totalling 18%, you need to earn a gross income of 21,342 (1786/mo, 411/wk, ~10.30/hr at 40hr/wk) to pay taxes and cover all your bills with almost nothing left over. If you want to fund an IRA account to the max annual limit (6500 at age 50+), you need to earn 27,842 (2320/mo, 534/wk, ~13.40/hr at 40hr/wk).
Assuming you flip once per week to make your nut, and you set an automatic trade trigger to sell when your holdings gain 3%, you'd have to front $14,100 and still not be able to fund that IRA. With $18,200 you'd be able to fund your IRA too. Finding volatile stocks isn't terribly difficult. Knowing when they're that undervalued, AND having multiple chunks of capital to gamble when Stock A doesn't burp on schedule, is the difficult part. You can make your $411 or $534/week nut only if your success rate is 100% at picking 3%-undervalued stocks, 52 times a year. In a deflating or post-slide stagnant market, maybe nothing can be expected to uptick promptly. So I'd guess if you don't have around $100,000 to work with, working the market can't keep you in Twinkies, even as a 40-hour-per-week job.