Here is the breakdown if you keep $20,000 and put it in an account earning 4% per year. You use this $20,000 in the account to pay your 0% loan. Each month the balance goes down.
The first column is the balance in your account. The center column is the interest earned each month. The third column is the loan balance.
As you can see, you earn $2,320.07 by using the 0% loan and investing your $20k. If you get a $1,000 rebate for paying cash, you really only earned $1,320.07 by going with the 0% loan... but you still MADE over $1k by going with the 0% loan instead of paying cash.
APY 0.04
MPY 0.003333333
Payment 333.33
$20,000.00 $66.67 19,666.67 1st year
$19,733.33 $65.78 19,333.33
$19,465.78 $64.89 19,000.00
$19,197.33 $63.99 18,666.67
$18,927.99 $63.09 18,333.33
$18,657.75 $62.19 18,000.00
$18,386.61 $61.29 17,666.67
$18,114.56 $60.38 17,333.33
$17,841.61 $59.47 17,000.00
$17,567.75 $58.56 16,666.67
$17,292.98 $57.64 16,333.33
$17,017.29 $56.72 16,000.00
$16,740.68 $55.80 15,666.67 2nd year
$16,463.15 $54.88 15,333.33
$16,184.69 $53.95 15,000.00
$15,905.30 $53.02 14,666.67
$15,624.99 $52.08 14,333.33
$15,343.74 $51.15 14,000.00
$15,061.55 $50.21 13,666.67
$14,778.42 $49.26 13,333.33
$14,494.35 $48.31 13,000.00
$14,209.33 $47.36 12,666.67
$13,923.36 $46.41 12,333.33
$13,636.44 $45.45 12,000.00
$13,348.56 $44.50 11,666.67 3rd year
$13,059.73 $43.53 11,333.33
$12,769.92 $42.57 11,000.00
$12,479.16 $41.60 10,666.67
$12,187.42 $40.62 10,333.33
$11,894.71 $39.65 10,000.00
$11,601.03 $38.67 9,666.67
$11,306.37 $37.69 9,333.33
$11,010.72 $36.70 9,000.00
$10,714.09 $35.71 8,666.67
$10,416.47 $34.72 8,333.33
$10,117.86 $33.73 8,000.00
$9,818.25 $32.73 7,666.67 4th year
$9,517.64 $31.73 7,333.33
$9,216.04 $30.72 7,000.00
$8,913.42 $29.71 6,666.67
$8,609.80 $28.70 6,333.33
$8,305.17 $27.68 6,000.00
$7,999.52 $26.67 5,666.67
$7,692.85 $25.64 5,333.33
$7,385.16 $24.62 5,000.00
$7,076.44 $23.59 4,666.67
$6,766.70 $22.56 4,333.33
$6,455.92 $21.52 4,000.00
$6,144.11 $20.48 3,666.67 5th year
$5,831.25 $19.44 3,333.33
$5,517.36 $18.39 3,000.00
$5,202.42 $17.34 2,666.67
$4,886.42 $16.29 2,333.33
$4,569.38 $15.23 2,000.00
$4,251.28 $14.17 1,666.67
$3,932.11 $13.11 1,333.33
$3,611.89 $12.04 1,000.00
$3,290.59 $10.97 666.67
$2,968.23 $9.89 333.33
$2,644.79 $8.82 0.00
$2,320.27
$2,320.27
In this example, I use $40,000 as the tractor price and use 3% as the interest yield. (Higher tractor price but lower interest yield.) As you can see, you earn $3,366.86 by investing and going with 0% loan. Again, subtract the $1,000 discount for paying cash and you can see you come out ahead by $2,366.86.
APY 0.03
MPY 0.0025
Payment 666.67
$40,000.00 $100.00 39,333.33 1st year
$39,433.33 $98.58 38,666.67
$38,865.25 $97.16 38,000.00
$38,295.75 $95.74 37,333.33
$37,724.82 $94.31 36,666.67
$37,152.46 $92.88 36,000.00
$36,578.68 $91.45 35,333.33
$36,003.46 $90.01 34,666.67
$35,426.80 $88.57 34,000.00
$34,848.70 $87.12 33,333.33
$34,269.16 $85.67 32,666.67
$33,688.16 $84.22 32,000.00
$33,105.72 $82.76 31,333.33 2nd year
$32,521.81 $81.30 30,666.67
$31,936.45 $79.84 30,000.00
$31,349.63 $78.37 29,333.33
$30,761.33 $76.90 28,666.67
$30,171.57 $75.43 28,000.00
$29,580.33 $73.95 27,333.33
$28,987.62 $72.47 26,666.67
$28,393.42 $70.98 26,000.00
$27,797.74 $69.49 25,333.33
$27,200.56 $68.00 24,666.67
$26,601.90 $66.50 24,000.00
$26,001.74 $65.00 23,333.33 3rd year
$25,400.07 $63.50 22,666.67
$24,796.91 $61.99 22,000.00
$24,192.23 $60.48 21,333.33
$23,586.05 $58.97 20,666.67
$22,978.35 $57.45 20,000.00
$22,369.12 $55.92 19,333.33
$21,758.38 $54.40 18,666.67
$21,146.11 $52.87 18,000.00
$20,532.31 $51.33 17,333.33
$19,916.97 $49.79 16,666.67
$19,300.10 $48.25 16,000.00
$18,681.68 $46.70 15,333.33 4th year
$18,061.72 $45.15 14,666.67
$17,440.21 $43.60 14,000.00
$16,817.14 $42.04 13,333.33
$16,192.52 $40.48 12,666.67
$15,566.33 $38.92 12,000.00
$14,938.58 $37.35 11,333.33
$14,309.26 $35.77 10,666.67
$13,678.37 $34.20 10,000.00
$13,045.90 $32.61 9,333.33
$12,411.85 $31.03 8,666.67
$11,776.21 $29.44 8,000.00
$11,138.98 $27.85 7,333.33 5th year
$10,500.16 $26.25 6,666.67
$9,859.75 $24.65 6,000.00
$9,217.73 $23.04 5,333.33
$8,574.11 $21.44 4,666.67
$7,928.88 $19.82 4,000.00
$7,282.03 $18.21 3,333.33
$6,633.57 $16.58 2,666.67
$5,983.49 $14.96 2,000.00
$5,331.78 $13.33 1,333.33
$4,678.44 $11.70 666.67
$4,023.47 $10.06 0.00
$3,366.86
$3,366.86
If any of my math is wrong, please let me know.