What can I do with US$10K that is a good investment?

If you don't have an emergency fund, I would put some or all of it into something like a money market account. It won't grow very much, but it's safe and is quick and easy to withdraw when needed.

Otherwise depends on your age and situation, but an index fund (S&P 500) is almost always the right choice. It's flexible, doesn't usually lock you in, and will generally do very well in the mid-to-long term. If we hit a recession you might get stuck holding the shares for several months to a few years. The last thing you want to do is panic sell in that situation.

If you have any debt, paying that down is a very smart move, especially if the debt is charging more interest than your investment can earn. Future you will thank you.

Pay down your debts first.

With zero information on your situation, it's difficult to say. If you have debt, paying that down/off is generally priority one. If you are debt-free, then you have options. Your age, stability, goals, and other factors would generally dictate what type of action to take. Were it me (early 40s, very low interest rate home loan), I'd put it into an index fund where I've already got some investments. In my case, I'm investing for retirement in about 25-30 years (as if I'll be able to do that, but one can hope).

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Bees.

VT. Don’t gamble on single stocks. But since capitalism rules and all of congress owns stocks, you can be fairly confident the market will go up in the long term 10+ years horizon. And compound interest does miracles.

An index that either tracks the top 500 companies or the total market. Look up a 3-fund portfolio if you want to go a little deeper.

Alternatively, max out an IRA if you haven't already this year and are in a position where you won't need that money until retirement.

Edit: I realized I'm assuming a lot about your situation. So instead, here's a general list of priorities that applies to more or less any situation. You should only proceed with a step if all the steps above it are achieved. Also keep in mind, I'm not a financial advisor just a random stranger on the internet sharing my personal financial strategy.

1. Pay your future-self first. Establish regular contributions to your retirement account and HSA if you have one, totalling between 3-5% of your compensation or whatever your company's matching policy is (That's not free money, it's part of your compensation package. Not claiming it is like waving a portion of your income).

2. Pay off all debt since interest is essentially paying a percentage-based monthly fee for owing money and we're not privileged enough for our assets to cover that expense.

3. Build and maintain a liquid (cash) holding as an emergency fund. This isn't for investing or expensive new toys, it's insurance that will cover your expenses for 6-12 months. Put it in a high-yield savings account or money market since it will be a significant sum and inflation will otherwise reduce its value over time.

4. Max out your retirement accounts to the contribution limit, your 401(k), IRA, and HSA if you have one. These accounts have tax advantages that essentially mean you can put more money towards retirement than you could in an individual trading account. This doesn't have to be one lump sum, you can divide it up into monthly contributions so long as you're on track for maxing your contribution limits by the end of the year.

5. Open an individual trading account with a broker (Vanguard, Fidelity, etc.) and invest in index funds (3-fund portfolios are reliable and low-cost). If you anticipate a significant expense over the next 10 years, i.e. a down payment for a house you can budget between this and the funds going towards Step 4 but keep in mind the tax advantages of retirement accounts means you're likely missing out on some retirement gains.

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There is no universally good investment - it all depends on your priorities, risk appetite and timeframe.

Put it in an IRA so you cant touch it and buy high dividedend yeilding stocks that reinvest in more shares and let it sit for the next decade and pray that there is a radical social change in out society so we can save the Planet and Poor from Billionaires.

Vanguard S&P 500 fund.

Depends on your risk tolerance.

A 4% savings account is “safe” but might not keep up with inflation.

An index fund might be “good”, but the value can go down.

I'll reply without knowing your situation fully. If you don't have an emergency fund that would cover several months worth of expenses that is probably the single most impactful thing you can do with $10k. A few high yield savings account offer rates around 4%, some of them have strings attached, so read how it works carefully. Think of this as insurance against unforseen expenses that you might otherwise have to put on a card and consequently pay interest for. Pick a number and always make sure you keep that account at that number.

If you already have an emergency fund, you have lots of options. Personally, I am onboard with the folks recommending index funds. I have an ETF that tracks the DOW and it has outperformed most of my individual stocks significantly over time.

Most importantly, strangers on the internet are likely not financial advisors and may not even know what they are doing. Take everything with a grain of salt and if you talk to any investment companies make sure you understand the difference and overlap between a financial advisor and a fiduciary.

Don't disagree about stuffing it in VTI... But, be aware that things can go up and down, so don't obsess over the value one you put it in. It's long term so it should go up over long term, but they're can be months sheets it goes down and even a year where it doesn't do well

There is already some good advise, so I will add some of dubious value that might make sense for some people. Buy a better car (or get a motorcycle). I live in the US, so having private transportation is a necessity. I have a car, but mostly I share it with my parents. I do use a motorcycle as my main commute and it is cheaper than a car's running costs. Just saying that $10k + sale of your current car could fetch you just about any other car. It is kind of hard to do a whole lot of life changing things with only $10k. Perhaps dental work if you need any.

So from what I've read after viewing this thread, I make a vanguard account, either get a money market fund or a brokered CD, put the money in, let it sit for awhile, and then profit years down the line?

High yield savings account at SoFi or Ally Bank will give you 4% right now.

Hmmm I see a distinct lack of CDs on here...

(Now I'm considering not renewing my 5% 9 month investment) Lol

Give it to me

Passive global technology index tracking fund

I like roboinvester accounts. You put money in, it automatically invests in stocks for you based on your current age and risk tolerance (which you can change whenever you like). I particularly like Wealthfront, and their app/website are really good. They’ll manage $10-15k for free, and then above that you pay a small fee out of your earnings for their service. If you use someone’s sign-up link, they’ll bump your managed amount by $5k. Comment back if you’re interested and I can share mine. Good luck with your investment, whatever you choose!