Semi Monthly Mortgage Calculator: 24 Payments vs Monthly

The saving depends on two things: how many half payments you send, and when they reach the balance.

Illustrative $400,000, 30-year fixed at 7.24%, Freddie Mac's PMMS 30-year average for the week of October 29, 2026. Principal and interest only, no fees. Computed by this site.

Read the rows in pairs. The monthly and semi-monthly held rows are identical, because the money reaches the balance on the same dates. Semi-monthly on receipt moves half the money forward by two weeks, and that is worth $1,473. The two biweekly rows differ by about $1,156 for the same reason, while the jump from either semi-monthly row to either biweekly row is roughly $146,000 or more. Timing is a rounding error; the extra payment does the work.

The model is deliberately plain. Interest runs on the posted balance for the time since the last posting, at the annual rate times that fraction of a year. Half payments arrive evenly, with the second half of each month landing on the due date. There are no fees, because no plan's fee is published here; if yours has one, take it off the saving.

Semi-monthly means twice a calendar month, so 24 payments. Biweekly means every two weeks, so 26. The two extra half payments are one full payment a year: $2,725.99 here, on top of the twelve you already owed. That is the entire reason biweekly shortens the loan and semi-monthly does not. Semi-monthly sends about $32,712 a year, the same as monthly. The site's biweekly mortgage payment calculator covers the thirteenth payment in depth, so this page sticks to the 24-payment case.

Regulation Z sets the vocabulary. Under 12 CFR 1026.36(c)(1), a periodic payment is an amount sufficient to cover principal, interest and escrow, if applicable, for a given billing cycle. A partial payment is any payment less than that. So one half of your mortgage bill is, by definition, a partial payment, even though you meant it to be part of a plan. Full periodic payments must be credited as of the date of receipt, with narrow exceptions. Partial payments get no such promise.

One more detail in the same paragraph of the rule matters if you pay in an unusual way. If a servicer sets written requirements for making payments and accepts a payment that does not meet them, it must credit that payment as of five days after receipt. A transfer sent to the wrong address or in the wrong form can therefore post later than you expect, so follow your servicer's payment instructions for any twice-monthly routine.

The official commentary to the rule lists what a servicer may do with a partial payment, to the extent that the law and your loan contract do not prohibit it:

• Credit it on receipt. The half reduces what you owe straight away.
• Return it to you. The money comes back, and the bill is still unpaid.
• Hold it in a suspense or unapplied funds account. The money sits, and the statement must show it.

The rule does not choose among these for you. No source reviewed for this page says which one a particular servicer uses for a semi-monthly plan, and an enrollment in a formal plan may be treated differently from two unannounced transfers. Only your servicer can say. The return option is worth a moment's thought: if a half bounces back late in the month, the full payment may not arrive on time.

Once held funds reach a periodic payment, the commentary says they must be treated as one, and credited accordingly. The CFPB's plain-language summary says the same: when that special account collects enough for a full payment, the servicer has to credit it.

Picture the month. The first half lands mid-month and waits. The second half lands on the due date, the two make one periodic payment, and it posts that day. To the loan, that is identical to sending $2,725.99 on the due date. This semi monthly mortgage calculator simulates that sequence step by step and does not simply copy the monthly row, and the two totals match at $581,357.32.

Meanwhile your $1,363.00 has left your account two weeks before it does the loan any good, and it earns you nothing while it waits. So a held plan is, if anything, slightly worse than keeping the half in your own savings until the due date. The rule at least keeps it visible: a held amount must be disclosed on the periodic statement where one is required.

If the servicer does credit each half on receipt, half the money reaches the balance about two weeks early. In the first month, interest is $2,412.86 on that basis against $2,413.33 on a monthly loan: 47 cents. That small gap repeats and compounds for thirty years to reach $1,473, or about 0.25% of the interest. The final payment arrives half a month sooner, at 719 half payments instead of 720.

That figure also relies on interest being charged on the posted balance for the days between postings. If your loan works out interest once a month, even an on-receipt credit might not produce this result, so ask.

Because a periodic payment includes escrow where it applies, half of your principal and interest is not half of your bill. If your lender collects for taxes and insurance, each half has to be half of the total payment on your statement, or the two together will fall short and sit unapplied. The tool leaves escrow out because it never touches the balance. The taxes and insurance schedule shows the full payment.

The table assumes the second half lands on the due date. Reverse the order and things go wrong. If the first half goes on the due date and the second two weeks later, the periodic payment is not complete until after it was due. The CFPB's summary says your statement must show late payment fees and the date you need to pay to avoid them, so read that line before you set any dates. If the first half is being held, the date that counts is the day the second half completes the payment, since that is when the funds become a periodic payment. The safe pattern is to send the first half before the due date and have the second arrive no later than the due date.

The semi-monthly saving stays small across every common loan, and the held-in-suspense saving stays at zero. Only biweekly changes the scale. As a share of total interest, the on-receipt saving runs from 0.23% to 0.37% in these five examples, and it is largest on the shortest loan. Try your own rate and term in the semi monthly mortgage calculator above.

Illustrative $400,000 fixed-rate loans, no fees. 7.24% and 6.60% are Freddie Mac's PMMS 30-year and 15-year averages for the week of October 29, 2026; 6.00% and 8.00% are round reference rates. Computed by this site.

• If I pay half my bill mid-month, do you credit it, return it or hold it?
• If you hold it, does interest keep running on the full balance until the second half arrives?
• Does my loan work out interest monthly, or by the day?
• Do you run a formal twice-monthly plan, and is there any fee to join or per payment?
• Which date must the full amount reach you by to avoid a late fee?

Get the answers in writing, then check a statement after the first month. If funds are being held, the statement rules require information about partial payments to appear there.

This builds the on-receipt schedule; the download button in the tool gives you the same figures as plain values. Put the inputs in B1 (400000), B2 (7.24%) and B3 (30).

1. Half payment. In B4 enter =-PMT(B2/12,B3*12,B1)/2. Microsoft's PMT function returns a negative number for a loan and covers principal and interest only, so the minus sign flips it. It returns $1,363.00.
2. Headers and opening balance. In row 5 type Date, Payment, Interest, Principal and Balance across columns A to E. In E6 enter =B1 as the opening balance, and leave the rest of row 6 empty.
3. First row. In row 7: C7 is =E6*$B$2/24, B7 is =MIN($B$4,E6+C7), D7 is =B7-C7 and E7 is =E6-D7.
4. Dates. Type your first two payment dates in A7 and A8. In A9 enter =EDATE(A7,1) and format it as a date, so each row is one month after the row two above it.
5. Fill down. Copy columns B to E to row 726, and column A from row 9 to row 726. That is 720 rows; MIN trims the final payment, and later rows go to zero.
6. Check it. =NPER(B2/24,-B4,B1) should return 718.92, so 719 payments.

Your first row should read $1,206.67 interest, $156.33 principal and a $399,843.67 balance, and payment 719 should be $1,252.60. For the held-in-suspense case you need no new sheet: it is the ordinary monthly schedule, which the amortization calculator Excel guide builds.

If you are paid twice a month and want the biweekly result, you do not need 26 payments. Add one-twelfth of a payment each month, $227.17 here, or $113.58 on each half. The illustrative loan then finishes in 283 payments and saves $147,044, close to the biweekly rows above. Those figures use the site's monthly schedule with extra principal, and the extra payments calculator runs your own. The CFPB's advice is to check whether your loan allows extra payments and make sure they are applied to principal rather than interest. Compare that with the $1,473 that timing alone can deliver at best: the same plan, with $227.17 more each month, does about a hundred times as much.