YTM is the most comprehensive yield measure because it accounts for three things:

- Coupon income
- Capital gain or loss (if bought below or above par)
- Reinvestment of coupons at the same rate

That last assumption — reinvesting coupons at the same YTM — is also its main weakness, because interest rates change over time. That's called **reinvestment risk**.

One key fact worth memorizing: **when a bond trades at par, current yield = approximate YTM = YTM.** They're only equal at par.