Each loan product prices off its own slice of the bond market, so they don't move in lockstep. A 15-year loan amortizes fast. Most of the principal comes back by around year ten, so investors treat it like shorter-term debt and price it closer to the short end of the Treasury curve. A 30-year pays down slowly in its early years, so it prices against longer-duration debt, historically the 10-year Treasury, though in practice a mortgage's expected life runs more like a blended five-to-seven-year duration once refinances and early sales are accounted for. Because the two products key off different points on the yield curve, a given day can move them by different amounts, or in different directions entirely. A 15-year rate shifting while the 30-year barely budges is completely normal. Each tracks its own reference yield. The underlying principle: a mortgage rate reflects two things investors care about, how quickly they expect their money back and what yield a comparable-duration alternative pays. Change either input and that specific product reprices, independent of the others. That's also why the spread between the 15-year and the 30-year widens and narrows over time instead of staying fixed. Nobody can promise which way any point on the curve heads next, but once you see that each product answers to its own slice of the market, the day-to-day drift makes sense.