Yield to maturity (YTM) is the bond's internal rate of return — the single discount rate that makes the present value of all future cash flows (coupons and principal) equal the bond's dirty price. Think of it as the bond's 'all-in' yield, but with an important catch: YTM assumes you can reinvest every coupon payment at the same YTM rate, which rarely happens in practice. Because YTM appears inside the discounting formula, there's no closed-form solution — it's solved numerically using methods like Newton-Raphson or bisection, similar to IRR calculations in Excel. Despite its limitations, YTM is the industry standard for comparing bonds because it captures both income and capital gains/losses in a single number.