Calculate mortgage prepayment savings from lump sums and recurring extra payments. See timing impact, lump-sum scenarios, and balance projection.
Mortgage prepayment — making payments beyond the required minimum — is one of the most effective strategies for reducing total interest cost and building wealth. A single $20,000 lump-sum prepayment on a $280,000 mortgage at 6.5% can save over $45,000 in interest and shave 3+ years off the loan.
The key insight is timing: prepayments made early in the loan save dramatically more than the same amount later, because the balance (and therefore interest charges) is higher in early years. A $20K prepayment in month 1 saves roughly 40% more interest than the same prepayment in year 5.
This calculator models both lump-sum and recurring prepayments with flexible timing. The lump-sum scenario table compares different amounts from $5K to $100K, while the timing analysis shows how delaying the prepayment reduces its effectiveness. Combine a lump sum with monthly extra payments for maximum acceleration. Check the example with realistic values before reporting.
Every prepayment dollar saves you more than one dollar in future interest — the savings multiple often reaches 2-3x. This calculator quantifies the exact return on prepayment, compares multiple amounts, and highlights the cost of delaying — giving you the data to make a confident decision. Keep these notes focused on your operational context.
Prepayment reduces principal directly. Interest saved = Standard schedule interest − Prepaid schedule interest. Savings multiple = Interest saved / Prepayment amount. Timing: earlier prepayment → more remaining months to compound the benefit.
Result: Interest saved: $47,300 — Years saved: 3.2 — Savings multiple: 2.4x — Payoff: 21.8 years
A $20K lump-sum prepayment on $280K at 6.5% saves $47,300 in interest (2.4x the prepayment!) and cuts 3.2 years off the loan. Applied now vs in year 3, the savings drop from $47,300 to $38,900 — demonstrating the cost of delay.
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On a typical 6-7% mortgage, every $10,000 prepaid early saves $20,000-30,000 in interest over the remaining term. The savings multiple ranges from 1.5x to 3x, depending on rate, remaining term, and when the prepayment is made.
Compare your mortgage rate to expected after-tax investment returns. At 6.5% mortgage vs 8-10% stock market average, investing might win mathematically. But mortgage prepayment is a guaranteed, risk-free return. Many advisors suggest a split approach: max out retirement account match, build emergency fund, then apply excess to mortgage.
As early as possible. The first half of a mortgage term is when balances are highest and interest charges are greatest. A prepayment in year 1 saves roughly 40-50% more interest than the same amount in year 10. Even delaying by one year reduces savings noticeably.
After a lump-sum prepayment, you typically have two options: (1) keep the same payment and pay off sooner, or (2) recast the loan for lower payments over the same term. Option 1 saves more interest overall. Option 2 provides cash flow relief. Most advisors recommend option 1 unless cash flow is a concern.
Recasting (re-amortization) is when the lender recalculates your monthly payment based on the new, lower balance while keeping the same rate and remaining term. This lowers your required payment. Unlike refinancing, recasting has no closing costs (typically a $250-500 fee) and does not change your rate.
Most conventional US mortgages allow unlimited prepayment without penalty. Some loans (older FHA, non-QM, commercial) may limit annual prepayment to 10-20% of the original balance. Check your loan agreement for any prepayment restrictions before making large payments.