Chapter 2: How bonds actually work
In 2022 the broadest yardstick of the US bond market, the Bloomberg US Aggregate index, returned −13.0%, its worst calendar year since the index began in 1976 (per market data). The word "safe" took a beating that year, and so did a lot of people who owned bond funds without knowing why they could fall. The strange part is how small the explanation turns out to be. The whole mechanism fits in the picture above, and by the end of this chapter you will be able to read it at a glance.
A loan with a receipt
A bond is a loan you make to a government or a company, written down as a tradable receipt. Three numbers are stamped on the receipt at birth and never change.
The face value is the amount that comes back at the end, typically $1,000 per bond. The coupon is the fixed interest the borrower pays along the way, named for the paper coupons people once clipped and mailed in. A 4.00% coupon on a $1,000 face value means $40 a year, usually paid in two $20 installments. The maturity is the date the face value returns and the loan ends.
Those three are carved in stone. The fourth number is not. The price is what the receipt trades for today, and it moves every day the market is open, because you are allowed to sell your receipt to someone else before maturity. Almost every confusing thing about bonds is some version of one fact: the loan's terms are fixed, and the receipt's price is not.
The reason a fixed loan changes price is competition from new loans. Picture a bond paying a 4% coupon in a world where new, otherwise identical bonds pay 5%. Nobody will pay you the full $1,000 for the old receipt when the bond counter next door hands out $50 a year instead of $40. To find a buyer, your price drops until the old bond's total deal, its $40 coupons plus the discount the buyer gets, matches the new 5% world. The same logic runs in reverse when rates fall: old receipts with fat coupons become prizes and their prices rise. No promise was broken in either direction. The borrower keeps paying $40 like clockwork. Only the resale price moved.
That is the seesaw. Rates on one seat, your bond's price on the other, the plank perfectly rigid: when one end goes up, the other comes down.
Duration: how far out your seat sits
The seesaw tells you the direction. Duration tells you the size, and it is the single most useful number in bond investing. FINRA states the rule of thumb in one sentence: for every 1-point change in interest rates, a bond's price moves in the opposite direction by about its duration number in percent, so a duration of 10 plus a 1-point rise means roughly a 10% price decline.
On the playground, duration is how far from the pivot your seat sits. A bond maturing in 13 weeks sits practically on the pivot; rates can swing all they like and the seat barely moves, because your $1,000 comes back in 13 weeks no matter what. A bond maturing in 30 years sits at the far end of a very long plank, and every rate wobble at the other end swings it hard. Longer maturity stretches the plank, and smaller coupons stretch it too, since more of your money waits at the far end.
Real funds publish their seat distance. The iShares Core U.S. Aggregate Bond ETF, the standard broad bond fund, reported an effective duration of 5.78 years, while the iShares 20+ Year Treasury Bond ETF reported 15.39 (both from the iShares fund pages, June 11, 2026). Run FINRA's rule on 2022, when rates rose hard and fast, and the receipts line up with the plank lengths: the aggregate index returned −13.0% that year, and the 20+ year Treasury fund returned −31.4% (iShares, calendar 2022). Nobody defaulted on those Treasuries. The far seat just sat a long way from the pivot.
The calculator above is the seesaw with numbers attached. Leave the dials where they start, a duration of 6 and a rate rise of 1.00 point, and the price change reads −6.0%: $10,000 becomes $9,400. Drag the seat or the rate and watch the arithmetic stay boring, which is the point. The 2022 disaster was not mysterious; it was this slider math applied to a year when rates moved by multiple points.
If rates rose and my bond fund fell, where did the money go?
Nowhere, in the sense that matters. No borrower vanished and no coupon went unpaid; the fund's holdings were repriced for a world where new bonds pay more. The fall is the market marking down old receipts so their deals match the new counter prices. And the same event has a second half that the account statement hides. When rates rise, every maturing bond inside a fund, and every new dollar you add anywhere, starts earning the new, higher rate. The markdown today and the better income tomorrow are one event seen from two sides. The loss only becomes permanent if you sell the old receipts after the markdown and walk away before the higher income arrives. Hold to maturity on an individual Treasury and the full face value comes back regardless of what the resale price did in between. Hold a fund and the conveyor of maturing bonds gradually swaps in the new rates. Sell at the bottom and you keep the first half of the event and hand the second half to a stranger.
Elaine, a retired teacher you will meet properly later in this guide, sold her bond fund near the 2022 bottom and has held cash ever since, scared of both directions. She did the most human thing possible with the half of the story she had. Chapters 6 and 12 walk through her receipts and what holding would have done, with dates attached.
Coupon, yield, and yield to maturity
Three words that sound interchangeable are doing three different jobs, and one example bond sorts them out. Dev, a 28-year-old developer with a house down-payment fund he refuses to gamble, pulled up a real-style Treasury quote in June 2026 and read it line by line: a Treasury note, 4.000% coupon, maturing May 2036, priced at 96.4, yield 4.45%. That quoted yield matches the 10-year Treasury rate of 4.45% on treasury.gov as of June 11, 2026.
| Word | Plain meaning | Dev's note |
|---|---|---|
| Face value | what comes back at maturity | $1,000 |
| Coupon | fixed yearly interest, set at issue, never changes | $40 a year (4.00% of face) |
| Price | what the receipt trades for today, quoted per $100 of face | 96.4, so $964 per bond |
| Current yield | coupon divided by today's price | $40 divided by $964, about 4.15% |
| Yield to maturity | the all-in annual return if held to 2036: every coupon plus the climb from $964 back to $1,000 | 4.45% |
| Duration | seat distance on the seesaw | about 8, by the rule of thumb |
The pattern to memorize: when a bond trades below face value, current yield beats the coupon, and yield to maturity beats them both, because the buyer also pockets the climb back to $1,000 at the end. Yield to maturity is the number that lets you compare any bond to any other, which is why it is the one printed in the quote.
Dev's takeaway after ten minutes with the quote screen: "The yield column already did the homework. Coupon is history, price is mood, yield to maturity is the actual deal on the table." Then he checked the one number the quote screen does not advertise, the duration, and found roughly 8. His down payment is 3 years away. A seat that swings about 8% per rate point is not a seat for 3-year money, and he knew it before buying anything. That single check, duration against calendar, is the habit this chapter exists to install.
What this means before you buy anything
The seesaw is not a reason to avoid bonds. It is the price tag on a trade that is often worth making: longer seats have generally paid higher yields, as Chapter 5's tour of the yield curve shows with June 2026 numbers, and the swings average out for money that genuinely stays put. The trouble in 2022 landed mostly on people who did not know which seat they were in. They held duration 6 or duration 15 while believing they held a savings account, and the gap between belief and plank length is where the panic lived.
If you read the Finvest ETFs & Funds Guide, its Chapter 7 introduced bond funds as a conveyor belt with no maturity date and promised that ladders, Treasury mechanics, and the yield curve would get their own guide. This is that guide, and the seesaw is its first tool: Chapters 5, 6, and 12 all lean on the picture you just learned.
Never own a bond or a bond fund whose duration you do not know. The number is one sentence of risk disclosure, printed free on every fund page, and it would have predicted nearly everything that shocked bond investors in 2022.
Where people go wrong
- Hearing "bonds" and filing them under "can't go down." A duration of 6 means roughly −6% per 1-point rate rise. Safe from default and safe from repricing are different kinds of safe.
- Judging a bond by its coupon. A 4% coupon bond priced at 96.4 and a zero-coupon bond can offer the same yield to maturity. The deal lives in the yield, never in the coupon alone.
- Selling after the markdown and missing the second half. The price drop and the higher forward yield arrive together. Elaine's 2022 sale, autopsied in Chapter 6, locked in the first and forfeited the second.
- Comparing a bond's yield to maturity against a savings APY without checking the seat. The bill on the pivot and the 30-year bond at the far end both quote a yield; only one of them can fall 15% on the way.
Key takeaways
- A bond is a loan with a tradable receipt: face value, coupon, and maturity are fixed at birth, and only the price moves.
- Prices move opposite to rates because old fixed coupons must be discounted or premiumed until they match what new bonds pay. The seesaw is rigid.
- Duration is seat distance: per FINRA's rule of thumb, a 1-point rate change moves price by about the duration number in percent. At the defaults, duration 6 and a 1.00-point rise, −6.0% turns $10,000 into $9,400.
- The 2022 receipts fit the rule: the aggregate index returned −13.0% (worst year since its 1976 start) and the 20+ year Treasury fund −31.4% (iShares, calendar 2022), with durations of 5.78 and 15.39 reported on the fund pages as of June 11, 2026.
- A rate rise marks down old bonds and raises what every new dollar earns; the loss is permanent only if you sell. Know your duration before you own anything.
Sources: FINRA on duration and rate changes · iShares Core U.S. Aggregate Bond ETF (AGG) · iShares 20+ Year Treasury Bond ETF (TLT) · Treasury daily yield curve · Bloomberg US Aggregate index 2022 calendar-year return, per market data · Finvest ETFs & Funds Guide