Mortgage Principal Calculator
Discover exactly how much of each mortgage payment builds your equity vs pays the bank. See the principal-interest split for any year of your loan, when the crossover happens, and how extra payments accelerate your equity growth.
Principal % of Payment Over Time
In year 1, only 12.3% of your payment is principal. By year 30, it is nearly 100%. The crossover (principal exceeds interest) happens at year 21.
The Principal-Interest Crossover Point
The crossover point is the exact month when your principal payment exceeds your interest payment — a financial milestone on your mortgage journey.
| Month | Principal | Interest | Principal % | Status |
|---|---|---|---|---|
| Month 240 | $1,152 | $1,177 | 49.5% | Interest wins |
| Month 241 | $1,159 | $1,170 | 49.8% | Interest wins |
| Month 242 (crossover) | $1,165 | $1,163 | 50.0% | Principal wins |
| Month 243 | $1,172 | $1,156 | 50.3% | Principal wins |
| Month 244 | $1,179 | $1,149 | 50.6% | Principal wins |
How to Use This Mortgage Principal Calculator
This calculator shows exactly how much of each mortgage payment goes to principal vs interest — and how that split changes every year of your loan.
Quick Results
Enter your Loan Amount, Interest Rate, Term, and Current Year of Loan. The calculator immediately shows your monthly payment breakdown: how many dollars go to principal, how many to interest, and what percentage each represents. The visual bar updates in real time as you change the current year.
Advanced: Growth Chart and Year Comparison
The "Principal Growth Chart" shows how the principal percentage of each payment increases over the loan term. "Year Comparison" gives a detailed table at years 1, 5, 10, 15, 20, 25, and 30 so you can see the acceleration. "Extra Payment Impact" calculates how additional monthly payments shift the principal curve forward.
Pro: Crossover Point, Velocity, and Tax Impact
The "Crossover Point" reveals the exact month when principal finally exceeds interest in your payment — typically around year 18-21 for a 30-year mortgage at current rates. "Principal Velocity" shows how fast equity builds through payments alone. "Tax Implications" tracks how your shrinking interest deduction affects your real after-tax mortgage cost over time.
How Principal and Interest Are Calculated
For payment number i:
Interest portion = Remaining Balance × Monthly Rate
Principal portion = Monthly Payment − Interest portion
New Balance = Old Balance − Principal portion
Where:
Monthly Rate = Annual Rate ÷ 12
n = Total months (term × 12)
At month 1: Interest is highest, principal is lowest
At month n: Principal is highest, interest is ~$0
Crossover: Month when principal portion > interest portion
Example: $350,000 Loan at 7.0% for 30 Years
How the principal/interest split changes for David
| Monthly Payment | $2,329 |
| Year 1, Month 1: Interest | $2,042 (87.7%) |
| Year 1, Month 1: Principal | $287 (12.3%) |
| Year 10: Interest | $1,732 (74.4%) |
| Year 10: Principal | $597 (25.6%) |
| Crossover Point (principal = interest) | Month 253 (~Year 21) |
| Year 21: Interest | $1,161 (49.9%) |
| Year 21: Principal | $1,168 (50.1%) |
| Year 30: Principal | $2,316 (99.4%) |
For the first 21 years, David pays more interest than principal each month. Only in year 21 does each payment finally put more toward his home than toward the bank. This is why paying extra early in the loan has such a dramatic impact.