People type this into search every day: biweekly mortgage calculator.
A biweekly plan takes half of the monthly principal-and-interest payment every two weeks. The CFPB mortgage key terms describe that schedule as 26 half payments, which is one extra monthly payment a year.
This page walks that arithmetic on the biweekly mortgage calculator. The numbers are labeled examples. They are not a payoff quote, and they are not personalized financial advice.
What the 26 debits actually are
A year has 52 weeks. Every two weeks is 26 debits. Half of a monthly payment, times 26, is 13 monthly payments. A normal year of the loan is 12.
The calculator starts from the same monthly payment as the mortgage payment calculator:
P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1)
P is the loan. r is the annual rate divided by 12. n is the months in the term. The biweekly debit is that monthly payment divided by 2. The extra thirteenth payment is applied as extra principal, spread as monthly payment ÷ 12 added to each month.
Interest in this model is charged once a month on a fixed rate. There is no fee and no prepayment penalty in the formula. A real note can have both. The CFPB’s servicing guide is the place to confirm that extra principal is applied to the balance.
Fig 1
Where the 13th payment comes from
Half the monthly payment, every two weeks
26 half payments equal 13 monthly payments. The calculator treats that extra one as principal.
Example 1: the calculator defaults
Inputs:
- loan amount: $336,000
- annual rate: 6.25%
- term: 30 years
Months in the term: 30 × 12 = 360
Monthly rate: 0.0625 ÷ 12 = 0.00520833…
Monthly principal and interest: $2,068.81
Biweekly debit: 2068.81 ÷ 2 = $1,034.40
Extra paid each year: the same $2,068.81
Extra added inside each month: 2068.81 ÷ 12 = $172.40 on the display. Twelve times that rounded figure is $2,068.80, one cent under the monthly payment, because the calculator divides the unrounded payment and then rounds the result.
Payoff if you send only the scheduled payment: 30y 0m inside this term.
Payoff with the extra: 24y 5m
Time saved: 5y 7m
Interest saved: $89,900.53
Calculator result
Biweekly mortgage payment
- Loan amount
- $336,000.00
- Annual interest rate
- 6.25%
- Loan term
- 30 years
$1,034.40
every two weeks
- Monthly principal and interest
- $2,068.81
- Extra paid each year
- $2,068.81
- Time saved
- 5y 7m
The balance path below uses the same two payments. Scheduled is $2,068.81 a month. Accelerated is $2,068.81 + $172.40.
Fig 2 · 1/2
Balance with and without the extra
$336,000 at 6.25%, sampled every 5 years
Remaining principal
- Scheduled
- With the 13th payment
| Point | Scheduled | With the 13th payment |
|---|---|---|
| 0y | $336k | $336k |
| 5y | $314k | $302k |
| 10y | $283k | $254k |
| 15y | $241k | $190k |
| 20y | $184k | $102k |
| 25y | $106k | $0.00 |
| 30y | $0.00 | $0.00 |
Both start at $336,000. At 15 years the scheduled balance is still $241,282.32.
With the extra, the balance is $0 by year 25. The scheduled loan still has $106,369.58.
Year 15 is the clearest gap. Scheduled balance $241,282.32. Accelerated balance $190,062.42. The loan with the extra is already $51,219.90 smaller, and it still has about nine years to go.
Fig 3 · 1/2
One year of the default loan
Twelve scheduled payments, then the thirteenth
12 payments
$24,825.72
13th payment
$2,068.81
Twelve payments of $2,068.81 are $24,825.72.
The thirteenth payment is another $2,068.81. That is the whole biweekly difference.
Check the shares against gross cash in that year: 24,825.72 + 2,068.81 = $26,894.53. The twelfth-payment block is 24825.72 ÷ 26894.53 = 92.3%. The extra is 7.7%.
Example 2: $300,000 at 6% for 30 years
This is the worked case on the calculator’s own guide.
Inputs: $300,000, 6%, 30 years.
Monthly payment: $1,798.65
Biweekly debit: $899.33
Extra each year: $1,798.65
Time saved: 5y 5m
Interest saved: $73,665.36
Payoff with the extra: 24y 7m
Calculator result
Biweekly mortgage payment
- Loan amount
- $300,000.00
- Annual interest rate
- 6%
- Loan term
- 30 years
$899.33
every two weeks
- Monthly principal and interest
- $1,798.65
- Extra paid each year
- $1,798.65
- Time saved
- 5y 5m
The time saved is close to Example 1. The dollars are smaller because the loan and the rate are both smaller. Interest saved fell by 89,900.53 − 73,665.36 = $16,235.17.
Example 3: a smaller loan at a higher rate
Inputs: $180,000, 6.5%, 30 years.
Monthly payment: $1,137.72
Biweekly debit: $568.86
Extra each year: $1,137.72
Time saved: 5y 10m
Interest saved: $52,353.77
Payoff with the extra: 24y 2m
A higher rate stretches the time saved a little, even on a smaller balance. The interest dollars are still well under the $336,000 case, because there is less principal to charge interest on.
Example 4: a larger loan at 7.25%
Inputs: $550,000, 7.25%, 30 years.
Monthly payment: $3,751.97
Biweekly debit: $1,875.98
Extra each year: $3,751.97
Time saved: 6y 5m
Interest saved: $202,800.99
Payoff with the extra: 23y 7m
The extra payment is large because the monthly payment is large. That is the pattern. The calculator does not apply a special jumbo rule. It runs the same monthly interest loop on a bigger balance.
Example 5: the same $336,000 on a 15-year term
Inputs: $336,000, 5.5%, 15 years.
I changed the term and used a lower rate than the 30-year default. A 15-year note is often priced differently. Type the rate from the offer you actually have.
Monthly payment: $2,745.40
Biweekly debit: $1,372.70
Extra each year: $2,745.40
Time saved: 1y 8m
Interest saved: $19,786.57
Payoff with the extra: 13y 4m
Calculator result
Biweekly mortgage payment
- Loan amount
- $336,000.00
- Annual interest rate
- 5.5%
- Loan term
- 15 years
$1,372.70
every two weeks
- Monthly principal and interest
- $2,745.40
- Extra paid each year
- $2,745.40
- Time saved
- 1y 8m
Compare that with Example 1. Same loan amount. The 15-year plan already pays the balance down fast, so the thirteenth payment has fewer years of interest to avoid. Time saved drops from 5y 7m to 1y 8m. Interest saved drops from $89,900.53 to $19,786.57.
Example 6: what if the rate falls to 4.5%
Hold the Example 1 loan and term. Change only the rate to 4.5%.
Monthly payment: $1,702.46
Biweekly debit: $851.23
Extra each year: $1,702.46
Time saved: 4y 4m
Interest saved: $46,526.11
Payoff with the extra: 25y 8m
The lower rate cuts the interest the extra payment can avoid. You also send a smaller thirteenth payment, because the monthly payment itself is smaller.
Example 7: what if the rate rises to 7.5%
Same $336,000, same 30 years, rate 7.5%.
Monthly payment: $2,349.36
Biweekly debit: $1,174.68
Extra each year: $2,349.36
Time saved: 6y 8m
Interest saved: $133,539.23
Payoff with the extra: 23y 4m
Against Example 1, the rate is 1.25 percentage points higher. Interest saved rises by 133,539.23 − 89,900.53 = $43,638.70. Time saved rises from 5y 7m to 6y 8m.
Fig 4 · 1/3
Interest saved on $336,000 over 30 years
Only the rate changes. The 13th payment is one monthly payment a year.
Interest saved
4.5%
$46,526.11
6.25%
$89,900.53
7.5%
$133,539.23
At 4.5% the interest saved is $46,526.11.
At 6.25% it is $89,900.53.
At 7.5% it is $133,539.23.
Example 8: a low rate on $250,000
Inputs: $250,000, 3%, 30 years.
Monthly payment: $1,054.01
Biweekly debit: $527.01
Extra each year: $1,054.01
Time saved: 3y 6m
Interest saved: $16,953.93
Payoff with the extra: 26y 6m
At 3%, a lot of each payment is already principal. The extra still shortens the loan. It just has less interest to erase. This is the edge of the idea. A biweekly plan is quieter when the rate is low.
Example 9: a 20-year term
Inputs: $280,000, 6%, 20 years.
Monthly payment: $2,006.01
Biweekly debit: $1,003.00
Extra each year: $2,006.01
Time saved: 2y 8m
Interest saved: $31,149.88
Payoff with the extra: 17y 4m
Put this next to Example 2, which is $300,000 at the same 6% for 30 years. The 30-year version saves $73,665.36 and 5y 5m. The 20-year version saves $31,149.88 and 2y 8m. Shorter remaining terms leave less interest on the table.
Example 10: twice a month is not every two weeks
This is the mix-up the calendar creates.
Take Example 1’s monthly payment, $2,068.81.
Every two weeks:
26 × (2,068.81 ÷ 2) = 13 × 2,068.81 = $26,894.53
Twice a month:
24 × (2,068.81 ÷ 2) = 12 × 2,068.81 = $24,825.72
The gap is one monthly payment, $2,068.81. That is the “Extra paid each year” line on the calculator.
A twice-a-month debit of the same half payment does not create a thirteenth payment. In this model the extra principal is then $0, time saved is 0, and interest saved is $0. You have matched the original schedule with more frequent transfers.
If you would rather pick the extra yourself, the mortgage extra payment calculator takes any monthly add-on. One twelfth of the monthly payment is the biweekly equivalent. The two tools stop the last month on slightly different balances, so read each result on its own page.
What a published fee range does to Example 1
The CFPB’s 2015 complaint against Nationwide Biweekly describes one company’s program, not a fee schedule for every servicer. The press release says the setup fee was up to $995, and processing fees were $84 to $101 a year.
Example 1’s interest saved is $89,900.53, and the accelerated payoff is 24y 5m. Round that enrollment up to 25 years and use the top of the published range:
995 + 25 × 101 = $3,520
89,900.53 − 3,520 = $86,380.53
The bottom of the range is 995 + 25 × 84 = $3,095, which leaves $86,805.53.
On this loan those fees do not erase the interest figure. They are still cash you pay on top of the extra principal. The same complaint says the marketing claimed people could save without paying more. The thirteenth payment is more. The fee is more again.
On the 15-year case in Example 5, interest saved is $19,786.57 and the payoff is 13y 4m. Using 14 years at the top of the range:
995 + 14 × 101 = $2,409
19,786.57 − 2,409 = $17,377.57
Still a fraction of the interest saved, and still a real fee. If a program keeps the first extra debit as its setup charge, that first debit never reaches principal. Ask the servicer before you enroll. You can also send the extra payment yourself and skip the program fee.
The examples side by side
| Example | Loan | Rate | Term | Biweekly debit | Time saved | Interest saved | Payoff |
|---|---|---|---|---|---|---|---|
| 1. Defaults | $336,000 | 6.25% | 30 years | $1,034.40 | 5y 7m | $89,900.53 | 24y 5m |
| 2. Guide case | $300,000 | 6% | 30 years | $899.33 | 5y 5m | $73,665.36 | 24y 7m |
| 3. Smaller loan | $180,000 | 6.5% | 30 years | $568.86 | 5y 10m | $52,353.77 | 24y 2m |
| 4. Larger loan | $550,000 | 7.25% | 30 years | $1,875.98 | 6y 5m | $202,800.99 | 23y 7m |
| 5. 15-year term | $336,000 | 5.5% | 15 years | $1,372.70 | 1y 8m | $19,786.57 | 13y 4m |
| 6. Lower rate | $336,000 | 4.5% | 30 years | $851.23 | 4y 4m | $46,526.11 | 25y 8m |
| 7. Higher rate | $336,000 | 7.5% | 30 years | $1,174.68 | 6y 8m | $133,539.23 | 23y 4m |
| 8. Low rate | $250,000 | 3% | 30 years | $527.01 | 3y 6m | $16,953.93 | 26y 6m |
| 9. 20-year term | $280,000 | 6% | 20 years | $1,003.00 | 2y 8m | $31,149.88 | 17y 4m |
| 10. Twice a month | $336,000 | 6.25% | 30 years | half, 24 times | 0 | $0 | 30y 0m |
Example 10 is the scheduled loan. There is no thirteenth payment to apply.
Open the biweekly mortgage calculator with your balance, rate, and years left. If the choice is between extra principal and another use of the cash, the mortgage overpayment vs index investing post runs that comparison on a different pair of formulas. Discount points are a separate upfront trade, covered in are mortgage discount points worth the cost?.