Principal — loan amortization

Pro workbook: Loan with extra payments, Compare, Formulas. Sample data, real formulas.

Loan amortization
Type the loan in the yellow cells. The payment and the whole schedule follow. Extra payments shorten it.
Amount borrowed250,000.00Monthly payment1,595.51With extra paymentsInterest each month = previous balance × rate ÷ 12, rounded to cents — the way a bank does it,
Annual interest rate5.90%Payments (scheduled)300Payments made235so the last payment absorbs the rounding instead of leaving 3 cents owing.
Term (years)25Total interest (scheduled)228,651.85Total interest167,796.40Year-end rows are shaded. The schedule stops on its own when the balance reaches zero.
First payment2026-10-01Total paid (scheduled)478,651.85Interest saved60,855.45Up to 480 payments (40 years).
Extra every month150.00Months saved65
Paid offApr 2046
#DatePaymentExtra (one-off)PrincipalInterestTotal paidInterest to dateBalance
1Oct 20261,745.51516.341,229.171,745.511,229.17249,483.66
2Nov 20261,745.51518.881,226.633,491.012,455.80248,964.78
3Dec 20261,745.51521.431,224.085,236.523,679.88248,443.35
4Jan 20271,745.51524.001,221.516,982.024,901.39247,919.35
5Feb 20271,745.51526.571,218.948,727.536,120.33247,392.78
6Mar 20271,745.51529.161,216.3510,473.047,336.68246,863.62
7Apr 20271,745.51531.761,213.7512,218.548,550.43246,331.86
8May 20271,745.51534.381,211.1313,964.059,761.56245,797.48
9Jun 20271,745.51537.011,208.5015,709.5610,970.06245,260.47
10Jul 20271,745.51539.651,205.8617,455.0612,175.92244,720.82
11Aug 20271,745.51542.301,203.2119,200.5713,379.13244,178.52
12Sep 20276,745.515,000.005,544.971,200.5425,946.0714,579.67238,633.55
13Oct 20271,745.51572.231,173.2827,691.5815,752.95238,061.32
14Nov 20271,745.51575.041,170.4729,437.0916,923.42237,486.28
15Dec 20271,745.51577.871,167.6431,182.5918,091.06236,908.41
16Jan 20281,745.51580.711,164.8032,928.1019,255.86236,327.70
17Feb 20281,745.51583.571,161.9434,673.6020,417.80235,744.13
18Mar 20281,745.51586.431,159.0836,419.1121,576.88235,157.70
19Apr 20281,745.51589.321,156.1938,164.6222,733.07234,568.38
20May 20281,745.51592.221,153.2939,910.1223,886.36233,976.16
21Jun 20281,745.51595.131,150.3841,655.6325,036.74233,381.03
22Jul 20281,745.51598.051,147.4643,401.1426,184.20232,782.98
23Aug 20281,745.51600.991,144.5245,146.6427,328.72232,181.99
24Sep 20281,745.51603.951,141.5646,892.1528,470.28231,578.04
25Oct 20281,745.51606.921,138.5948,637.6529,608.87230,971.12
26Nov 20281,745.51609.901,135.6150,383.1630,744.48230,361.22
27Dec 20281,745.51612.901,132.6152,128.6731,877.09229,748.32
28Jan 20291,745.51615.911,129.6053,874.1733,006.69229,132.41
29Feb 20291,745.51618.941,126.5755,619.6834,133.26228,513.47
30Mar 20291,745.51621.991,123.5257,365.1935,256.78227,891.48
31Apr 20291,745.51625.041,120.4759,110.6936,377.25227,266.44
32May 20291,745.51628.121,117.3960,856.2037,494.64226,638.32
33Jun 20291,745.51631.201,114.3162,601.7038,608.95226,007.12
34Jul 20291,745.51634.311,111.2064,347.2139,720.15225,372.81
Compare rates and terms
Monthly payment and total interest for the loan amount on the Loan sheet, across rates and terms. No extra payments here.
Monthly payment10 yrs15 yrs20 yrs25 yrs30 yrs
3.90%2,519.261,836.721,501.811,305.831,179.17
4.90%2,639.431,963.991,636.111,446.951,326.82
5.90%2,762.972,096.161,776.681,595.511,482.84
6.90%2,889.842,233.121,923.271,751.031,646.50
7.90%3,020.002,374.722,075.571,913.011,817.01
Total interest1015202530
3.90%52,311.6880,609.01110,434.40141,748.23174,501.38
4.90%66,732.19103,517.40142,666.43184,083.96227,654.05
5.90%81,556.97127,308.70176,404.39228,651.85283,822.86
6.90%96,781.24151,961.06211,584.68275,309.56342,740.12
7.90%112,399.52177,449.63248,136.36323,902.60404,124.86
Yellow rates in the first column are editable; the second table reads them. The row matching your rate is highlighted.
Term headers in row 11 are numbers (years) so the formulas can read them.
How the formulas work
Every formula in this workbook, in plain words. Interest is computed month by month, not with IPMT, so you can see it. Formulas are shown without the leading = sign.
WhereFormulaWhat it does
Loan · Monthly payment-PMT(B4/12, B5*12, B3)Excel's PMT with the rate per month and the number of months. PMT returns a negative (money going out); the minus sign flips it.
Loan · Interest (row)ROUND(I11*$B$4/12, 2)Last month's balance × annual rate ÷ 12, rounded to cents like a lender does. Rounding here means the final payment absorbs the odd cents.
Loan · Payment (row)MIN($E$3+$B$7+N(D12), I11+F12)Scheduled payment plus the monthly extra plus any one-off in column D — but never more than what's owed (balance + this month's interest), so the last payment is exact. N() turns an empty extra into 0.
Loan · Principal (row)C12-F12Whatever isn't interest reduces the balance.
Loan · Balance (row)ROUND(I11-E12, 2)Previous balance minus principal paid. Hits exactly 0.00 on the last row.
Loan · # (row)IF(I11<=0, "", 12)The row number appears only while there's a balance left, which is how the schedule stops itself. The money columns return 0 on those rows, hidden by the number format, so SUMs never meet a blank text.
Loan · Date (row)IF(A12="", "", EDATE($B$6, 11))First payment date plus n months.
Loan · Payments madeCOUNTIF(I12:I491, ">0") + IF(COUNTIF(I12:I491, 0)>0, 1, 0)Rows with a balance still owing, plus the one row where it reaches zero.
Loan · Interest savedE5-H5Scheduled total interest minus the interest actually paid with extras.
Loan · Paid offINDEX(B12:B491, H4)The date on the last payment row.
Compare · payment grid-PMT($A5/12, B$11*12, Loan!$B$3)Same PMT with the rate from the row and the term (years, in row 11) from the column.
Compare · interest gridB5*B$11*12 - Loan!$B$3Payment × number of payments minus the amount borrowed.