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Estimate the effect of one lump-sum prepayment on an equal-payment CNY mortgage.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Use this calculator to estimate the effect of one lump-sum principal payment on an equal-payment mortgage denominated in Chinese yuan (CNY). It compares the modeled interest still due under the original schedule with interest under a revised schedule. The difference is labeled interest saved. You can choose to keep the modeled monthly payment and shorten the remaining term, or keep the remaining term and lower the monthly payment.
The original principal and the one-time prepayment are entered in units of CNY 10,000. For example, enter 100 for a CNY 1,000,000 original loan and 20 for a CNY 200,000 prepayment. The annual rate is entered as a percentage, and the two dates are selected by month. Result amounts are shown in CNY, rounded to whole yuan; the new remaining term is shown in years to one decimal place.
Equal-payment amortization means the scheduled principal-and-interest payment stays level when the rate and schedule stay unchanged, while the share applied to interest generally falls as principal is repaid. The calculator converts the entered annual rate to a monthly rate by dividing by 12. For principal P, monthly rate i, and n monthly installments, the modeled payment A is:
A = P × i × (1 + i)n ÷ [(1 + i)n − 1]
After p installments, the modeled balance is Bp = P × [(1 + i)n − (1 + i)p] ÷ [(1 + i)n − 1]. The one-time payment is subtracted from that balance, then the chosen option recalculates the remaining schedule.
The method follows the equal-payment formula described in a People’s Bank of China notice for individual housing loans. The calculator uses this formula as a mathematical model; it does not retrieve a lender’s account balance or payment schedule. Read the notice and formula (October 14, 1998; checked September 29, 2026).
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use the original amount borrowed, in CNY 10,000, the original term in years, and the annual interest rate as a percentage. Keep these figures consistent with the same loan and repayment plan. Do not enter the current balance as the original amount.
Set the first repayment month and the planned lump-sum prepayment month. The model treats the whole-month difference between these dates as installments already made. It does not use a day-of-month, a posting date, or a lender’s accrued-interest figure.
Enter the planned lump sum in CNY 10,000, then select a recalculation approach. “Monthly payment unchanged, shorten term” keeps the original modeled payment. “Term unchanged, reduce monthly payment” keeps the remaining number of installments.
Record the original remaining interest, new remaining interest, interest saved, new monthly payment, and new remaining term. Change only the approach to compare the two modeled outcomes on the same loan, date, rate, and prepayment amount.
With CNY 1,000,000 original principal, a 30-year term, 4.2% annual rate, first payment in January 2020, and a CNY 200,000 lump sum in January 2025, the model counts 60 elapsed monthly installments. Its estimated balance before the lump sum is about CNY 907,365. With the term held at 25 remaining years, the model estimates a new payment of about CNY 3,812 per month and interest savings of about CNY 123,365. With the modeled payment held near CNY 4,890, it estimates a shorter remaining term and savings of about CNY 274,347. These are outputs of the stated assumptions, not a lender quote.
Use cases
See how the tool fits into real work and everyday tasks.
If the goal is to see how a lump sum could reduce the scheduled payment while retaining the remaining timeline, select the option that keeps the term unchanged. Compare the new payment with the current modeled payment.
If the current modeled payment remains affordable and the question is how much sooner the balance could be repaid, select the option that keeps the monthly payment unchanged. Focus on the new remaining term and modeled interest difference.
Save both estimates as discussion points, then ask the loan provider which recalculation options apply to the contract and what balance and charges would apply on the intended date.
Q&A
Find concise answers to common questions and confusing cases.
Enter the original principal. The calculator estimates the balance at the selected prepayment month from the original term, rate, and elapsed months. Substituting today’s balance as the original amount changes the modeled history.
No. It means the number of installments remaining at the selected prepayment month is retained. In the preset example, 60 months have elapsed from a 30-year schedule, so the modeled remaining term is 25 years.
The model uses month-level dates, one unchanged annual rate, and an equal-payment schedule. A lender’s balance or payoff figure can use contract-specific dates, rate changes, accrued interest, rounding, and applicable charges that this estimate does not include.
It is the difference between modeled interest remaining on the original schedule and modeled interest on the revised schedule. It is not the amount of cash returned, does not include interest already paid, and does not subtract fees or other costs.
Notes
Review scope, result limitations, and important precautions before use.
This is an estimate based on entered assumptions, not individualized financial advice, a payoff quote, or a promise of lender treatment. Confirm the contract terms and obtain a dated calculation from the loan provider before acting.
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