BYTETOOLS

Mortgage Recast Calculator

See what a lump-sum principal payment does to your mortgage: the recast payment over the remaining term versus keeping the payment and shortening the loan.

$1,590.57
New payment after recast
$259.68
Monthly saving
2 mo
Fee break-even
$41,023.63
Interest saved by recasting

Three paths, side by side

Doing nothing, recasting to a lower payment, and paying the lump sum but keeping the same payment
MeasureNo changeRecastLump sum, same payment
Starting balance$285,000.00$245,000.00$245,000.00
Monthly payment$1,850.25$1,590.57$1,850.25
Time to payoff26 yr 1 mo26 yr18 yr 10 mo
Total interest$292,278.65$251,255.02$171,752.22
Interest saved—$41,023.63$120,526.43
Months removed—1 mo7 yr 3 mo

Cash-flow relief comes from recasting; the bigger interest saving comes from keeping the old payment. The $350.00 recast fee pays for itself after 2 months of the lower payment.

Amortisation preview — first 60 months

Month-by-month balances under each of the three paths
MonthNo changeRecast balanceKeep-payment balance
1$284,634.13$244,685.47$244,425.79
2$284,266.35$244,369.30$243,848.59
3$283,896.65$244,051.49$243,268.38
4$283,525.03$243,732.02$242,685.15
5$283,151.47$243,410.89$242,098.89
6$282,775.97$243,088.09$241,509.57
7$282,398.51$242,763.60$240,917.18
8$282,019.09$242,437.42$240,321.71
9$281,637.69$242,109.54$239,723.14
10$281,254.30$241,779.96$239,121.45
11$280,868.92$241,448.66$238,516.62
12$280,481.53$241,115.64$237,908.64
13$280,092.12$240,780.88$237,297.50
14$279,700.68$240,444.38$236,683.17
15$279,307.20$240,106.12$236,065.64
16$278,911.68$239,766.10$235,444.90
17$278,514.10$239,424.31$234,820.93
18$278,114.44$239,080.74$234,193.71
19$277,712.70$238,735.38$233,563.22
20$277,308.87$238,388.22$232,929.45
21$276,902.94$238,039.26$232,292.37
22$276,494.89$237,688.48$231,651.98
23$276,084.72$237,335.87$231,008.25
24$275,672.41$236,981.42$230,361.17
25$275,257.95$236,625.13$229,710.72
26$274,841.34$236,266.98$229,056.88
27$274,422.56$235,906.97$228,399.63
28$274,001.59$235,545.08$227,738.96
29$273,578.43$235,181.31$227,074.85
30$273,153.07$234,815.64$226,407.28
31$272,725.49$234,448.07$225,736.23
32$272,295.69$234,078.58$225,061.69
33$271,863.65$233,707.17$224,383.64
34$271,429.36$233,333.82$223,702.05
35$270,992.80$232,958.53$223,016.91
36$270,553.97$232,581.29$222,328.21
37$270,112.86$232,202.08$221,635.92
38$269,669.45$231,820.90$220,940.02
39$269,223.73$231,437.73$220,240.50
40$268,775.69$231,052.56$219,537.34
41$268,325.31$230,665.39$218,830.51
42$267,872.59$230,276.20$218,120.00
43$267,417.51$229,884.99$217,405.79
44$266,960.06$229,491.74$216,687.86
45$266,500.23$229,096.44$215,966.19
46$266,038.00$228,699.08$215,240.76
47$265,573.36$228,299.65$214,511.56
48$265,106.30$227,898.14$213,778.56
49$264,636.81$227,494.54$213,041.74
50$264,164.88$227,088.84$212,301.08
51$263,690.49$226,681.02$211,556.56
52$263,213.63$226,271.08$210,808.17
53$262,734.28$225,859.01$210,055.88
54$262,252.44$225,444.79$209,299.67
55$261,768.09$225,028.41$208,539.52
56$261,281.22$224,609.86$207,775.41
57$260,791.81$224,189.13$207,007.32
58$260,299.85$223,766.21$206,235.23
59$259,805.33$223,341.09$205,459.12
60$259,308.23$222,913.75$204,678.97
$245,000.00
Balance after the lump sum
14.0%
Payment drop
$120,526.43
Interest saved keeping the payment

A recast applies your lump sum to principal and then re-amortises the reduced balance over the remaining original term at the same rate, so the payment falls but the payoff date does not move. Keeping the old payment on the reduced balance leaves the payment where it is and shortens the term instead — that path always saves more interest. Both are compared here against doing nothing. Figures cover principal and interest only; escrowed taxes and insurance are excluded. Check whether your loan is eligible, as many government-backed mortgages are not. Estimates for planning, not financial advice.

What is the Mortgage Recast Calculator?

The ByteTools Mortgage Recast Calculator shows what happens after you put a lump sum against your principal.

  • Three-way comparison: do nothing, recast, or keep the payment and shorten the term
  • Recast payment re-amortised over the remaining term, not a fresh full term
  • Interest saved, months removed and total interest for every path
  • Recast fee break-even in months of the lower payment
  • Optional override for your actual payment when it differs from the scheduled one
  • Month-by-month balance preview and a full CSV export

How to use the Mortgage Recast Calculator

  1. 1

    Enter your current balance, interest rate and the remaining term in years.

  2. 2

    Enter the lump sum you plan to pay against principal and the recast fee your lender charges.

  3. 3

    Tick the override box if your actual monthly payment differs from the one the tool derives.

  4. 4

    Compare the three columns: no change, recast, and lump sum with the same payment.

  5. 5

    Download the month-by-month comparison as a CSV.

About the Mortgage Recast Calculator

The ByteTools Mortgage Recast Calculator shows what happens after you put a lump sum against your principal. A recast re-amortises the reduced balance over the remaining original term at the same rate, so the payment drops but the payoff date does not move — and the tool compares that against keeping the old payment, which shortens the loan instead.

Both paths are shown against doing nothing, with the new payment, total interest, time to payoff, interest saved and months removed for each. A recast fee break-even tells you how many months of the lower payment it takes to earn the fee back, and the whole three-way comparison exports to CSV.

All amortisation is computed in your browser with nothing uploaded, so your loan details stay on your device. Figures cover principal and interest only — escrowed taxes and insurance are excluded — and are planning estimates, not financial advice.

Frequently asked questions

What is a mortgage recast?

You pay a lump sum against principal and the lender re-amortises what is left over the remaining original term at the same interest rate. Your monthly payment falls, the rate and term stay the same, and there is no refinance, no new appraisal and no credit check.

Is a recast better than just paying extra principal?

It depends what you want. Paying the lump sum and keeping your old payment always saves more interest and pays the loan off sooner. A recast trades some of that saving for lower monthly cash flow, which is worth it if the payment relief is what you actually need.

How much does a mortgage recast cost?

Lenders typically charge a flat administrative fee of a few hundred, far less than refinancing costs because nothing is underwritten again. The break-even figure here divides that fee by your monthly saving to show how many months it takes to pay for itself.

Does a recast change my interest rate?

No. A recast keeps your existing rate and term and only recalculates the payment against a smaller balance. If you want a different rate you need a refinance, which involves underwriting, closing costs and a new loan.

Which loans can be recast?

Most conventional mortgages allow it, usually with a minimum lump sum, but many government-backed loans do not. Check with your servicer before making the payment, because a lump sum without a recast simply shortens the loan rather than lowering the payment.

Is my loan information uploaded?

No. Balances, rates and the entire amortisation schedule are computed in your browser, and the CSV is generated on your device, so nothing about your mortgage is transmitted.

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