Learn how to precisely calculate monthly payments, compare loan options, and make the smartest home buying decision
Buying a home is the biggest financial decision most people will ever make. Understanding how mortgage calculations work puts you in a stronger negotiating position. This guide covers the two core repayment methods, key factors that affect your monthly payments, and how to use calculator tools to quickly compare different loan options.
Equal monthly installment is the most common repayment method. Your monthly payment stays the same, but the ratio of principal to interest shifts over time — interest dominates early on, while principal makes up a larger share in later months.
Best for: Salaried workers with stable income who prefer predictable monthly payments for budgeting. This is also the default method recommended by most banks.
With equal principal, you pay a fixed amount of principal each month plus interest on the remaining balance. As a result, your monthly payment decreases over time — highest in the first month, lowest in the last.
Best for: Borrowers with strong early repayment capacity who want to minimize total interest. If you expect your income to decrease or plan to pay off the loan early, equal principal is more economical.
Let's compare both methods with a ¥1,000,000 loan at 4.2% annual interest:
| Item | Equal Installment (30yr) | Equal Principal (30yr) |
|---|---|---|
| First Month Payment | ¥4,891 | ¥6,167 |
| Last Month Payment | ¥4,891 | ¥2,790 |
| Total Repayment | ¥176.10,000 | ¥163.40,000 |
| Total Interest | ¥76.10,000 | ¥63.40,000 |
| Interest Difference | Equal principal saves ¥127,000 | |
The loan term has a massive impact on both monthly payments and total interest. Here's a comparison using a ¥1,000,000 loan at 4.2% with equal installment:
| Term | Monthly Payment | Total Interest | Total Repayment |
|---|---|---|---|
| 15 years | ¥7,505 | ¥35.10,000 | ¥135.10,000 |
| 20 years | ¥6,165 | ¥47.90,000 | ¥147.90,000 |
| 25 years | ¥5,434 | ¥63.00,000 | ¥163.00,000 |
| 30 years | ¥4,891 | ¥76.10,000 | ¥176.10,000 |
Stretching from 15 to 30 years reduces the monthly payment by ¥2,614 (35% less), but total interest jumps by ¥410,000 (117% more). If you can afford an extra ¥2,600 per month, a 15-year term saves a staggering amount in interest.
But don't forget about opportunity cost — the extra ¥2,600 per month could be invested for returns that exceed the additional interest. That's where an ROI calculator comes in handy for a comprehensive evaluation.
Since October 2019, China has used the LPR (Loan Prime Rate) pricing mechanism. Mortgage Rate = LPR + Spread (in basis points).
Key points to know:
For every 0.1% rate drop, total interest on a ¥1M 30-year loan decreases by roughly ¥22,000. Monitoring LPR trends and locking in rates when they're low — or choosing a floating rate — can be a smart strategy.
Is early repayment worth it? It depends on several factors:
When early repayment makes sense:
When early repayment is not recommended:
While manual calculation works, it's inefficient when comparing multiple scenarios. We recommend using an online calculator:
Steps:
We suggest calculating 2-3 different scenarios for comparison. For example, compare a "¥1M commercial loan for 30 years" against a "¥600K provident fund + ¥400K commercial loan" combination to see how much interest you can save.
Mortgage calculations aren't complicated, but understanding the logic can save you a significant amount of money. The keys are: understanding the difference between repayment methods, choosing the right loan term, monitoring rate changes, and planning your prepayment strategy. Use calculator tools to compare multiple scenarios and let data drive your decisions.
Whether you're preparing to buy a home or looking to optimize an existing loan, the RiseTop Mortgage Calculator delivers precise results to help you manage your mortgage with ease.