About the Amortization
Every fixed-rate loan payment is split between interest and principal, and that split shifts dramatically over the life of the loan - early payments are mostly interest, later payments are mostly principal. Our Amortization Schedule Calculator generates the full year-by-year breakdown so you can see exactly where your money goes.
How It Works
The calculator runs the standard amortization formula month by month for the full loan term, tracking the interest and principal portion of every payment and the remaining balance after each one. It then summarizes the results into a yearly table and chart so the full-term picture is easy to read at a glance.
Formula & Methodology
Interest for any given month is calculated on the remaining balance at that point (balance × monthly rate), and whatever's left of the fixed payment after covering that interest becomes principal. Because the balance shrinks a little more each month, the interest portion shrinks too, which means the principal portion grows - the front-loaded interest structure isn't a special rule lenders apply, it's simply the mathematical consequence of charging interest on a shrinking balance every period.
Step-by-Step: Calculating It By Hand
- 1For each month, multiply the current remaining balance by the monthly interest rate to find that month's interest charge.
- 2Subtract the interest charge from the fixed monthly payment to find that month's principal reduction.
- 3Subtract the principal reduction from the balance to find the new remaining balance.
- 4Repeat for every month of the loan term, then summarize into yearly totals for the schedule.
Examples
Early years
On a $250,000, 30-year loan at 6.5%, the first year's payments are roughly two-thirds interest and one-third principal.
Later years
By year 25 of the same loan, that ratio flips dramatically - most of each payment goes to principal, which is why home equity builds slowly at first and quickly later.
Advantages
- Shows the full year-by-year breakdown, not just a single monthly payment figure
- Makes the front-loaded interest structure of amortizing loans visually clear
- Useful for understanding how extra payments early in the loan have outsized impact
- Works for any fixed-rate loan amount, rate, and term combination
Common Mistakes
- Assuming principal and interest are split evenly across every payment (they're not, especially early on)
- Being surprised at how little equity builds in the first several years of a mortgage
- Not realizing extra payments early in the schedule save far more interest than the same extra payment made later
- Confusing an amortization schedule with a simple payment calculator - this shows the full breakdown over time
Edge Cases to Watch For
- Any extra payment beyond the required amount goes entirely to principal, accelerating the schedule and reducing all future interest - this is why extra payments early in the loan have outsized impact.
- A loan with a very short term (like a 5-year auto loan) has a much less dramatic interest-to-principal shift than a 30-year mortgage, simply because there's less time for the balance to compound.
- Refinancing resets the amortization schedule entirely, meaning the new loan starts back at the interest-heavy beginning regardless of how far along the original loan was.
- Rounding on the final payment (to bring the balance to exactly zero) is standard practice and can make the last payment slightly different from all prior ones.
Common Use Cases
- Seeing exactly how a specific loan's payments break down over its full term
- Understanding how quickly (or slowly) you'll build equity in a mortgage
- Deciding when extra payments would have the most impact
- Reviewing loan terms before signing