The yield curve refers to the chart of current pricing on US Treasury Debt instruments, by maturity. The US Treasury currently issues debt in maturities of 1, 2, 3, and 6 months—and 1, 2, 3, 5, 7, 10, 20, and 30 years. If you bought $1,000 of the 10-year bonds with an interest rate of 2%, then you would pay $1,000 today, then receive $20 in interest ($1,000 x 2%) at the end of years 1-9, and receive $1,020 (representing $20 interest + your original $1,000) at the end of year 10. Current interest rates are shown on the US Treasury's website.

The interest rates that these bonds pay reflect two main factors: 1) the Federal Funds rate, and 2) expectations of future returns.

The Federal Feds rate (aka the fed funds rate) is a short-term target rate set by the US Federal Reserve and is the interest rate that banks use to lend/borrow from the each other overnight. This is almost always the "interest rate" you hear about on the news when there are headlines about rates rising or falling, and this rate sets the foundation of almost all other economic interest rates.

Since the fed funds rate is the rate at which you can effectively lend cash to the US Government overnight, this rate serves as the foundation of the yield curve—it is essentially a US Treasury bond with a 1-day maturity. When the Federal Reserve changes this rate, all other rates tend to change accordingly as w

The Federal Reserve sets the overnight interest rate—but the interest rates on Treasury bonds from 1-month to 30-years are set by the market and fluctuate with investor demand. For example, assume that the Fed Funds rate is 2%. This indicates that investors can lend money to the US Government overnight and receive a 2% annualized rate of return. If that is true, then we would generally assume a 1-month Treasury bond rate to be a little higher than 2%. This is because investors value optionality. They like having access to their money in case something better comes along, so they require extra return if they're going to lock up their money for a full month - otherwise instead of buying a 1-month bond, they would just buy the overnight bond every night for a month.

To better illustrate this - assume that the 3-month Treasury bond rate is 2.5%. Again, this says that an investor can lend their money to the US Government for three months and receive 2.5% annualized interest in return. If you are the investor, what rate would you need to receive in order to extend this loan to the US Government from three months to ten years? Ten years is a long time, and many more attractive investment opportunities may come up over those ten years. If you've committed your money to a US Treasury bond and won't get it back for ten years, you need to be getting paid enough to be comfortable that nothing substantially more attractive is going to come along in the meantime. Otherwise, why not just keep investing in the three month bond every three months?

Accordingly, it is almost always the case that as the maturity period increases, the interest rate on Treasury bonds increases as well. This is called a normal yield curve, and is illustrated in the rates below, from Jan 2017.

Yield inversion is the term used when long term rates are lower than short term rates. This happens when investors are nervous about the future and expect short term rates to fall. When so many investors think rates are going to fall, they will crowd into the longer-dated bonds to try to lock in the 'high' rate for as long as possible.

For example, assume that the economy is roaring, and the Fed Funds rate is 4%, 3-month rate is 4.5%, and the 10-year rate is 6%. This would be quite normal, as described and illustrated above. Now assume that you are an investor who thinks that the economy is weakening, and likely to slow down in the near future. If this were to happen, you would predict that the Federal Reserve would need to lower short term interest rates in order to juice the economy a bit (i.e., basic monetary policy). If this were true, and you expected all rates to go down in the near future, you would invest more in long-term bonds (10, 20, 30-year), in order to 'lock in' those good rates. When many investors begin to do this, the rates of long term bonds fall, and in extreme cases may actually fall below the rate of short term bonds, causing an inverted yield curve.

Inverted yield curves are very rare, occurring only once a decade or so, and almost always immediately before a recession.

The current yield curve is shown below, along with the prior two month-ending curves:

The above chart shows the shape of the current yield curve. The front of the curve is steeply inverted, not at all like the normal curve shown previously.

The traditional measure of whether or not the yield curve is said to be normal, flat, or inverted is by examining the relationship between the 3-month and 10-year rates. The below chart shows the value of the 10-year bond (normally high) minus the value of the 3-month bond (normally low). We should expect the result to be a positive number, given a normally sloped yield curve. This is observed in the chart below. The majority of the data points are above 0%, shaded blue. The few periods where the yield curve was inverted are shaded red. Note that you can zoom in/out by dragging any area of the chart.

As before, prior economic recessions are highlighted as gray vertical bands. Notice that every single recession is preceded by a yield curve inversion.

Again, in a normal rate environment the 10-year rate is much higher than the 3-month rate, so this spread will be a positive number. As the spread moves closer to zero, and as it turns negative, it reflects the 10-year rate falling below the three month rate, indicating that investors expect future economic slowdown in the near term. As you can see by the shaded recession areas, investors have almost always been correct in this prediction. For the last 50 years, every yield curve inversion has been soon followed by economic recession.

We now have all the data we need - but in order to get a better sense of the historical trend, we can present it in a slightly different way. The chart above showed the historical 10-Year to 3-Month yield spread, including the average spread over that time of 1.38%. Below is the same chart, but with the data centered around that average 1.38% value. In order to get a sense of the volatility of the data, bands of +/- 1 standard deviation from the average are added as well. The dashed red line indicates where the yield curve becomes inverted as the 10-year rates are lower than 3-month rates.

Statistically, about two-thirds of the time the yield spread should be within 1 standard deviation from the average. Broadly speaking, when the spread is below the average it indicates a selling opportunity, as flat/negative spreads are correlated with economic recessions and market downturns. Conversely, highly positive yield spreads tend to be buying opportunities, as they typically occur right after a rate-reduction policy response to a market downturn (i.e., when the market tanks the fed cuts short term rates to 0, and so yield spreads are high).

Lastly, we'll flip the y-axis on this chart in order to be consistent with "up" being values where the market is overvalued, in line with other models throughout this site. This is purely cosmetic.

The New York Federal Reserve uses the yield curve to calculate the probability that the US economy will be in a recession in 12 months. (Note: the calc is whether or not there we will be in a recession 12 months from the time of the calculation, not anytime in the subsequent 12 months). Currently, the NY Fed assigns a 46% probability that the US will be in a recession in October 2024.

So far we've seen that yield curve inversions are highly correlated with subsequent economic recessions - but what can that tell us about stock market valuation? Does a yield curve inversion also precede market crashes? Do periods of 'normal' sloping yield curves correlate with positive market returns?

The below two charts illustrate the 10Year-3Month yield curve spread mapped over S&P500 returns. The data series is just the price of the S&P500, with the color of the line highlighted red during periods of yield curve inversion. Clearly, you can see strong correlation where periods of inversion tend to precede stock market devaluations.

No single metric is illustrative of the health or relative valuation entire market, or can perfectly predict upcoming recessions. Here are some reasons why this yield curve model doesn't show the full picture:

The unprecedented monetary policies implemented by central banks worldwide, particularly in response to the financial crisis of 2008, may be influencing the traditional dynamics of the yield curve. Programs like quantitative easing, which involve large-scale purchases of long-term securities, have driven down long-term interest rates and can potentially cause yield curve inversions, or materially change the yield curve from historic trends. As a result, an inverted yield curve in today's context might not necessarily signify an impending recession, but rather, it could be a byproduct of these non-traditional monetary policies.

In an increasingly interconnected global economy, U.S. Treasury yields are often affected by international economic conditions and global investor sentiment. Strong international demand for U.S. Treasuries, particularly long-term ones, can drive down long-term yields, potentially leading to a yield curve inversion. This situation could occur even in the absence of recessionary pressures in the U.S. economy. For example, during periods of global economic uncertainty, international investors may see U.S. government bonds as a safe haven, increasing demand and lowering yields. This activity alone doesn't seem likely to invert our yield curve, but it is an additional (and increasingly important) dynamic that should be considered.