The monthly payment is the number everyone asks for and the least informative number on the page. It says what leaves your account; it says nothing about where it goes. That is what the schedule is for, and you only need the first twelve rows to see the shape of the whole thing.
Take a $360,000 loan over 30 years at 6.75%. The payment is about $2,335. In month one, $2,025 of that is interest and $310 is principal. You pay $2,335 and own $310 more of your house. This is not a trick; it is just what a fixed payment against a large balance looks like.
The crossover point
Each month the balance falls slightly, so the interest charge falls slightly, so slightly more of the same payment goes to principal. The line crosses — more principal than interest in a single payment — around year 19 on a 30-year loan at this rate. Earlier at lower rates, later at higher ones.
This is why an extra payment early is worth several late ones: money that reduces the balance in year two removes the interest it would have generated for the remaining 28 years. The same money in year 25 removes five years of interest. The schedule makes this visible in a way the payment figure never can.
What to look for in the first twelve rows
Three things. The interest share of the first payment tells you what the loan costs while the balance is still whole. The principal growth month over month tells you how fast that improves. And the balance after twelve payments, compared with what you paid in that year, tells you the real first-year cost of owning the loan — a number worth knowing before you sign for it.