For buy-and-hold strategies: leverage (borrowing to invest) can be used to increase returns. The Sharpe ratio of a portfolio is a measure of it's risk/reward trade-off; there's a theorem that given a set of assets with fixed known distributions and ability to borrow at the risk-free rate, the Kelly optimal allocation is a leveraged version of the portfolio with highest Sharpe ratio. You can calculate that optimal leverage in various ways.
In practice, we don't know future Sharpe ratios (only the past), we don't have assets with fixed known distributions (to the extent there is a distribution, it likely changes over time), and there's other idiosyncratic risks to leverage.
Using past data, however, is highly suggestive that at least some leverage is a great idea. For instance, a 40/60 stock/bond portfolio has higher Sharpe ratio than a 100% stock portfolio in almost all historical models since bonds and stocks have low correlation. It's not unreasonable to assume that low correlation will hold going forward. If I leverage up a stock/bond portfolio to the same volatility as the corresponding 100% stock portfolio, I see a 2-4% increase in yearly returns depending on time period. This is easily achievable by buying leveraged ETFs.
Naive Kelly models will usually recommend more risk than the stock market, so if your risk tolerance is even higher the (potentially naive and misleading) math is on your side. Be careful if you might need the money soon: these models assume you're never withdrawing!
My opinion: ~1.5-2.5x leverage on stock/bond portfolios looks reasonable for long-term investors, although it really depends on the assets -- short term treasuries for example are so stable that even 10x leveraging isn't crazy.
In the real world, you can leverage by:
- Buying leveraged ETFs. These work just like buying stocks or regular non-leveraged ETFs. Vanguard doesn't allow these, so I use Fidelity. I might recommend SSO and TMF, along with international + extended market diversification. Since the leverage on these is set daily, they eliminate some of the tail risk of leveraging. Downsides: volatility decay in sideways markets and ETFs can simply fail to track their (leveraged) index.
- Using margin accounts. This is where your broker lends you money, using your other investments as collateral. Rates are often really bad/not worth it -- be careful. Also they'll sell your other investments if you become overly leveraged due to a downturn (a "margin call") -- which means forced selling during a downturn, which can cause you to miss out on any recovery. I don't like this.
- Directly taking on debt / counter-factually not paying off debt. If you take out a mortgage instead of paying cash for a house, the money you saved can be considered to be "on loan" at the mortgage rate. Investing it is then a form of leveraging. This is bad if the rate is too high, but mortgage rates are really low right now.
- Futures. These allow higher leverage than ETFs and adoption of various strategies if you're willing to monitor them daily -- for instance, you can leverage/deleverage on a daily basis with no (additional) tax penalty. Great for getting really high leverage, e.g. for stable investments like treasuries. Downsides: your positions will be closed if you run out of margin -- which means you can be forced out of the market during a bad enough downturn, potentially missing the recovery. For high-leverage strategies, this means you probably need to monitor daily and de-lever as appropriate. Gains from futures are immediately taxed at 60% short-term 40% long-term capital gains, introducing tax drag that you wouldn't have with ETFs.
- Options. I don't know much about these. Here's a book talking about passive indexing approaches using options, which I haven't read: https://www.amazon.com/Enhanced-Indexing-Strategies-Utilizing-Performance/dp/0470259256.
- Other stuff (box spread financing?)
You can kind of backtest various strategies for yourself using e.g.:
Keep in mind that the past doesn't predict the future, and naive back-testing might not track historical reality perfectly or may be missing some idiosyncratic risks of leveraging certain ways.
For your maximal laziness, here's an ~1.9x leveraged ETF allocation I made up just now that's around 40/60 world stock market/long-term bonds: 36% TMF, 16% SSO, 8% VXF, 40% VXUS. Full disclosure: Lots of people would think this is a terrible allocation since "everyone knows" the bond market is due to crash due to current low interest rates.
For increasing salary vs investing: do these really funge against each other? Why not both? Generically I'd think income should dominate before you have a lot invested, and then investment strategy becomes important once your yearly average investment returns become similar in scale to your yearly income.
The concept of leverage is not complicated. How it affects volatility drag is, or at least seems so to me when I hear ppl explain it. There is a disconnect between how my bran conceptualizes the abstract percentages vs actually holding an asset.
So, the basic idea for an unleveraged investment is your geometric returns are lower than arithmetic returns because of volatility. E.g. if you have $100, gain 10% one period and lose 5% the next, the arithmetic average return is 2.5% per period, calculated as (10+(-5)/2 but you actually only have $104.5, a return of 2.25% per period, because you are losing 5% of a bigger number than you are gaining 10% on. Easy enough.
But let's say you leverage 2x. Assume no interest to keep it simple. Then this is 20% gain and 10% loss. You have $108. A bigger gain than in the above example, but not 2x as big. Or at least that's what I see articles online saying. But this doesn't make sense to me when I try to conceptualize it as actually holding an asset. Let's say I buy one share of the stock using my own money and one share using a loan. I hold exactly the two shares for the two periods regardless of what the price does, then sell them at the end and pay off the loan. My portfolio is 200, goes to 220 (10% gain), then goes to 209 (5% loss). Then I sell, pay off the loan, and I have $109, not $108. The problem comes if I am not allowed to have a loan too large compared to my assets and have to sell at a bad time. So if the 5% drop happens first, I have $190, of which 100 is borrowed. Have to sell $10 of stock to bring my loan to parity with my own investment. Then I have $180, of which 90 is borrowed, and can only make $18 when the market moves 10% up, instead of the 19 I'd have if I held on to everything. So then my return really is only 8% instead of 9%, because I was forced to maintain constant leverage ratio.
So among ETFs, investing on margin, and futures, which allows me to remain closest to the buy and hold strategy? Or do I face roughly the same constraint no matter what?