Coupon, current yield and YTM are different
Coupon rate applies to face value. Current yield divides annual coupon by the current market price. Yield to maturity also accounts for the price-to-face-value gain or loss if all cash flows are paid as scheduled.
Why YTM rises below face value
A bond priced below face value returns face value at maturity. That discount becomes part of the return, so the solved YTM can exceed the coupon rate. Above face value, a premium reduces YTM.
What YTM assumes
The conventional calculation assumes you hold to maturity, all contractual payments are received, and coupons can be reinvested at the same yield. That makes it a comparison metric, not a promised return.
Assess risk and taxes separately
Credit quality, liquidity, call features, duration, taxation and settled accrued interest can change the real outcome. Read the offer document and evaluate YTM alongside those risks.
Model it with your own numbers
Use the calculator before changing payments, transferring debt or relying on a projection.