额外还款计算器 — 公式

Impact of Extra Mortgage Payments

Extra payments applied to principal reduce the balance faster, saving interest and shortening the loan term.

New Payoff Formula

New Months = log(PMT / (PMT - P x r)) / log(1 + r)

Where PMT is the total monthly payment (base + extra), P is the loan balance, and r is the monthly rate.

Why Extra Payments Are So Effective

  • Early in a mortgage, most of each payment goes to interest
  • Extra principal reduces the balance that accrues interest
  • The effect compounds: less interest means more of future payments go to principal
  • Even small extra amounts make a significant difference over decades

    • Strategies

  • Round up to the nearest hundred
  • Apply annual bonuses or tax refunds
  • Match extra payments to raises or eliminated expenses

    • 计算示例

    A $300,000 loan at 7% for 30 years with an extra $300/month.

    1. Base payment: $1,995.91
    2. Total payment with extra: $1,995.91 + $300 = $2,295.91
    3. Original payoff: 360 months (30 years)
    4. New payoff: approximately 263 months (about 22 years)
    5. Months saved: 360 - 263 = 97 months (about 8 years)
    6. Original total interest: $418,528
    7. New total interest: approximately $303,726
    8. Interest saved: approximately $114,802