The schedule collapses when every spare dollar hits principal
A mortgage is just an interest clock running against an unpaid balance — the faster you shrink that balance, the fewer ticks you pay for. This tool runs the same loan three ways — contractual minimum, every monthly surplus poured onto principal, and HELOC chunking — and shows how much of the famous "pay it off in a decade" is simply the discipline of directing cash flow at the balance.
| Month | Payment | Interest | Principal | Extra | Balance |
|---|---|---|---|---|---|
| 1 | $1,896 | $1,625 | $271 | $3,000 | $296,729 |
| 2 | $1,896 | $1,607 | $289 | $3,000 | $293,440 |
| 3 | $1,896 | $1,589 | $307 | $3,000 | $290,134 |
| 4 | $1,896 | $1,572 | $324 | $3,000 | $286,809 |
| 5 | $1,896 | $1,554 | $342 | $3,000 | $283,467 |
| 6 | $1,896 | $1,535 | $361 | $3,000 | $280,106 |
| 7 | $1,896 | $1,517 | $379 | $3,000 | $276,728 |
| 8 | $1,896 | $1,499 | $397 | $3,000 | $273,330 |
| 9 | $1,896 | $1,481 | $415 | $3,000 | $269,915 |
| 10 | $1,896 | $1,462 | $434 | $3,000 | $266,481 |
| 11 | $1,896 | $1,443 | $453 | $3,000 | $263,029 |
| 12 | $1,896 | $1,425 | $471 | $3,000 | $259,557 |
| 13 | $1,896 | $1,406 | $490 | $3,000 | $256,067 |
| 14 | $1,896 | $1,387 | $509 | $3,000 | $252,558 |
| 15 | $1,896 | $1,368 | $528 | $3,000 | $249,030 |
| 16 | $1,896 | $1,349 | $547 | $3,000 | $245,483 |
| 17 | $1,896 | $1,330 | $566 | $3,000 | $241,917 |
| 18 | $1,896 | $1,310 | $586 | $3,000 | $238,331 |
| 19 | $1,896 | $1,291 | $605 | $3,000 | $234,726 |
| 20 | $1,896 | $1,271 | $625 | $3,000 | $231,102 |
| 21 | $1,896 | $1,252 | $644 | $3,000 | $227,457 |
| 22 | $1,896 | $1,232 | $664 | $3,000 | $223,793 |
| 23 | $1,896 | $1,212 | $684 | $3,000 | $220,110 |
| 24 | $1,896 | $1,192 | $704 | $3,000 | $216,406 |
| 25 | $1,896 | $1,172 | $724 | $3,000 | $212,682 |
| 26 | $1,896 | $1,152 | $744 | $3,000 | $208,938 |
| 27 | $1,896 | $1,132 | $764 | $3,000 | $205,174 |
| 28 | $1,896 | $1,111 | $785 | $3,000 | $201,389 |
| 29 | $1,896 | $1,091 | $805 | $3,000 | $197,584 |
| 30 | $1,896 | $1,070 | $826 | $3,000 | $193,758 |
| 31 | $1,896 | $1,050 | $846 | $3,000 | $189,912 |
| 32 | $1,896 | $1,029 | $867 | $3,000 | $186,045 |
| 33 | $1,896 | $1,008 | $888 | $3,000 | $182,156 |
| 34 | $1,896 | $987 | $909 | $3,000 | $178,247 |
| 35 | $1,896 | $966 | $930 | $3,000 | $174,317 |
| 36 | $1,896 | $944 | $952 | $3,000 | $170,365 |
| 37 | $1,896 | $923 | $973 | $3,000 | $166,392 |
| 38 | $1,896 | $901 | $995 | $3,000 | $162,397 |
| 39 | $1,896 | $880 | $1,016 | $3,000 | $158,381 |
| 40 | $1,896 | $858 | $1,038 | $3,000 | $154,342 |
| 41 | $1,896 | $836 | $1,060 | $3,000 | $150,282 |
| 42 | $1,896 | $814 | $1,082 | $3,000 | $146,200 |
| 43 | $1,896 | $792 | $1,104 | $3,000 | $142,096 |
| 44 | $1,896 | $770 | $1,126 | $3,000 | $137,970 |
| 45 | $1,896 | $747 | $1,149 | $3,000 | $133,821 |
| 46 | $1,896 | $725 | $1,171 | $3,000 | $129,650 |
| 47 | $1,896 | $702 | $1,194 | $3,000 | $125,457 |
| 48 | $1,896 | $680 | $1,216 | $3,000 | $121,240 |
| 49 | $1,896 | $657 | $1,239 | $3,000 | $117,001 |
| 50 | $1,896 | $634 | $1,262 | $3,000 | $112,739 |
| 51 | $1,896 | $611 | $1,285 | $3,000 | $108,453 |
| 52 | $1,896 | $587 | $1,309 | $3,000 | $104,145 |
| 53 | $1,896 | $564 | $1,332 | $3,000 | $99,813 |
| 54 | $1,896 | $541 | $1,355 | $3,000 | $95,457 |
| 55 | $1,896 | $517 | $1,379 | $3,000 | $91,079 |
| 56 | $1,896 | $493 | $1,403 | $3,000 | $86,676 |
| 57 | $1,896 | $469 | $1,427 | $3,000 | $82,249 |
| 58 | $1,896 | $446 | $1,450 | $3,000 | $77,799 |
| 59 | $1,896 | $421 | $1,475 | $3,000 | $73,324 |
| 60 | $1,896 | $397 | $1,499 | $3,000 | $68,825 |
| 61 | $1,896 | $373 | $1,523 | $3,000 | $64,302 |
| 62 | $1,896 | $348 | $1,548 | $3,000 | $59,755 |
| 63 | $1,896 | $324 | $1,572 | $3,000 | $55,182 |
| 64 | $1,896 | $299 | $1,597 | $3,000 | $50,585 |
| 65 | $1,896 | $274 | $1,622 | $3,000 | $45,963 |
| 66 | $1,896 | $249 | $1,647 | $3,000 | $41,316 |
| 67 | $1,896 | $224 | $1,672 | $3,000 | $36,644 |
| 68 | $1,896 | $198 | $1,698 | $3,000 | $31,946 |
| 69 | $1,896 | $173 | $1,723 | $3,000 | $27,223 |
| 70 | $1,896 | $147 | $1,749 | $3,000 | $22,475 |
| 71 | $1,896 | $122 | $1,774 | $3,000 | $17,701 |
| 72 | $1,896 | $96 | $1,800 | $3,000 | $12,901 |
| 73 | $1,896 | $70 | $1,826 | $3,000 | $8,074 |
| 74 | $1,896 | $44 | $1,852 | $3,000 | $3,222 |
| 75 | $1,896 | $17 | $1,879 | $1,344 | $0 |
The dramatic curves are not the product of any special account — they are the product of routing your whole surplus at the principal, month after month. Extra principal does that for free on the loan you already hold. HELOC chunking adds an offset and a borrowed lump sum on top, but it only pulls ahead when the HELOC's average-daily-balance float clears its higher rate; the moment its rate climbs, plain extra payments catch back up. The lever that matters is the surplus itself.
Model assumptions, all adjustable above: the same monthly surplus (net income minus expenses) is applied across the extra-principal and HELOC cases; the HELOC charges interest on its balance net of the average daily offset; rates are held constant (a real HELOC floats); the schedule is capped at 360 months. This is a teaching instrument, not financial advice.