Abzahlung eines Darlehens
B(0) | Darlehensbetrag (Schulden zur Zeit t = 0) |
t | Zeit in Monaten nach Aufnahme des Darlehens |
a | monatliche Zahlrate ( a = Z + b) |
p % | Zinssatz p.a. |
Z | monatliche Zinsen (Z = k*B(t) mit k = p/1200) |
b | monatlicher Abtrag |
tD | gesamte Darlehenszeit |
B(t) | Schulden zur Zeit t |
> restart; with(plots):
f:= t -> B(t):
diff(f(t), t) = k*f(t) - a;
diff(f(t), t) = k*f(t) - a;
Lösung dieser Differentialgleichung:
> dsolve(%, B(t));
Zur Zeit t = 0 wird der gesamte Darlehensbetrag geschuldet:
> lsg:= %:
subs({B(t)= B[0], t= 0}, %);
Berechnung der Konstanten _C1:
> _C1:= (solve(%, _C1));
Die zur Zeit t noch bestehenden Schulden B(t):
> B(t):= simplify(rhs(lsg));
Die monatliche Zahlrate a in Abhängigkeit von der gewünschten Darlehenszeit tD:
> solve(B(t) = 0, a):
a:= subs(t= t[D], %);
Beispiel: Darlehen 10.000 EUR; Zinssatz 7%; zurückzuzahlen in insgesamt 8 Jahren
> B[0]:= 10000: # Darlehensbetrag
p:= 7: # Zinssatz p.a.
k:= evalf(p/1200):
t[D]:= 8*12-1: # Darlehenszeit in Monaten
a:= round(a); # monatlicher Zahlbetrag
k:= evalf(p/1200):
t[D]:= 8*12-1: # Darlehenszeit in Monaten
a:= round(a); # monatlicher Zahlbetrag
Diskrete Rechnung in monatlichen Schritten:
> t:= 0: Z:= 0: b:= 0:
b_ges:= 0: Z_ges:= 0:
S:= B[0]:
printf("t S b b_ges Z Z_ges\n");
printf("%3.0f %9.2f %7.2f %9.2f %7.2f %9.2f\n",
t, S, b, b_ges, Z, Z_ges);
P[1]:= [0, 0]:
while (S > 0) do
t:= t+1: # Zeit in Monaten
Z:= k*S: # Zinsen im jeweiligen Monat
b:= a - Z: # Abtrag im jeweiligen Monat
if (b > S) then b:= S; fi:
S:= S - b: # jeweils noch verbleibende Schulden
Z_ges:= Z_ges + Z:
b_ges:= b_ges + b:
P[t+1]:= [t, Z_ges]:
printf("%3.0f %9.2f %7.2f %9.2f %7.2f %9.2f\n",
t, S, b, b_ges, Z, Z_ges);
od:
S:= B[0]:
printf("t S b b_ges Z Z_ges\n");
printf("%3.0f %9.2f %7.2f %9.2f %7.2f %9.2f\n",
t, S, b, b_ges, Z, Z_ges);
P[1]:= [0, 0]:
while (S > 0) do
t:= t+1: # Zeit in Monaten
Z:= k*S: # Zinsen im jeweiligen Monat
b:= a - Z: # Abtrag im jeweiligen Monat
if (b > S) then b:= S; fi:
S:= S - b: # jeweils noch verbleibende Schulden
Z_ges:= Z_ges + Z:
b_ges:= b_ges + b:
P[t+1]:= [t, Z_ges]:
printf("%3.0f %9.2f %7.2f %9.2f %7.2f %9.2f\n",
t, S, b, b_ges, Z, Z_ges);
od:
t | S | b | b_ges | Z | Z_ges |
0 | 10000.00 | 0.00 | 0.00 | 0.00 | 0.00 |
1 | 9921.33 | 78.67 | 78.67 | 58.33 | 58.33 |
2 | 9842.21 | 79.13 | 157.79 | 57.87 | 116.21 |
3 | 9762.62 | 79.59 | 237.38 | 57.41 | 173.62 |
4 | 9682.57 | 80.05 | 317.43 | 56.95 | 230.57 |
5 | 9602.05 | 80.52 | 397.95 | 56.48 | 287.05 |
6 | 9521.06 | 80.99 | 478.94 | 56.01 | 343.06 |
7 | 9439.60 | 81.46 | 560.40 | 55.54 | 398.60 |
8 | 9357.67 | 81.94 | 642.33 | 55.06 | 453.67 |
9 | 9275.25 | 82.41 | 724.75 | 54.59 | 508.25 |
10 | 9192.36 | 82.89 | 807.64 | 54.11 | 562.36 |
11 | 9108.98 | 83.38 | 891.02 | 53.62 | 615.98 |
12 | 9025.12 | 83.86 | 974.88 | 53.14 | 669.12 |
13 | 8940.76 | 84.35 | 1059.24 | 52.65 | 721.76 |
14 | 8855.92 | 84.85 | 1144.08 | 52.15 | 773.92 |
15 | 8770.58 | 85.34 | 1229.42 | 51.66 | 825.58 |
16 | 8684.74 | 85.84 | 1315.26 | 51.16 | 876.74 |
17 | 8598.40 | 86.34 | 1401.60 | 50.66 | 927.40 |
18 | 8511.56 | 86.84 | 1488.44 | 50.16 | 977.56 |
19 | 8424.21 | 87.35 | 1575.79 | 49.65 | 1027.21 |
20 | 8336.35 | 87.86 | 1663.65 | 49.14 | 1076.35 |
21 | 8247.98 | 88.37 | 1752.02 | 48.63 | 1124.98 |
22 | 8159.09 | 88.89 | 1840.91 | 48.11 | 1173.09 |
23 | 8069.69 | 89.41 | 1930.31 | 47.59 | 1220.69 |
24 | 7979.76 | 89.93 | 2020.24 | 47.07 | 1267.76 |
25 | 7889.31 | 90.45 | 2110.69 | 46.55 | 1314.31 |
26 | 7798.33 | 90.98 | 2201.67 | 46.02 | 1360.33 |
27 | 7706.82 | 91.51 | 2293.18 | 45.49 | 1405.82 |
28 | 7614.78 | 92.04 | 2385.22 | 44.96 | 1450.78 |
29 | 7522.19 | 92.58 | 2477.81 | 44.42 | 1495.19 |
30 | 7429.07 | 93.12 | 2570.93 | 43.88 | 1539.07 |
31 | 7335.41 | 93.66 | 2664.59 | 43.34 | 1582.41 |
32 | 7241.20 | 94.21 | 2758.80 | 42.79 | 1625.20 |
33 | 7146.44 | 94.76 | 2853.56 | 42.24 | 1667.44 |
34 | 7051.13 | 95.31 | 2948.87 | 41.69 | 1709.13 |
35 | 6955.26 | 95.87 | 3044.74 | 41.13 | 1750.26 |
36 | 6858.83 | 96.43 | 3141.17 | 40.57 | 1790.83 |
37 | 6761.84 | 96.99 | 3238.16 | 40.01 | 1830.84 |
38 | 6664.29 | 97.56 | 3335.71 | 39.44 | 1870.29 |
39 | 6566.16 | 98.12 | 3433.84 | 38.88 | 1909.16 |
40 | 6467.46 | 98.70 | 3532.54 | 38.30 | 1947.46 |
41 | 6368.19 | 99.27 | 3631.81 | 37.73 | 1985.19 |
42 | 6268.34 | 99.85 | 3731.66 | 37.15 | 2022.34 |
43 | 6167.90 | 100.43 | 3832.10 | 36.57 | 2058.90 |
44 | 6066.88 | 101.02 | 3933.12 | 35.98 | 2094.88 |
45 | 5965.27 | 101.61 | 4034.73 | 35.39 | 2130.27 |
46 | 5863.07 | 102.20 | 4136.93 | 34.80 | 2165.07 |
47 | 5760.27 | 102.80 | 4239.73 | 34.20 | 2199.27 |
48 | 5656.87 | 103.40 | 4343.13 | 33.60 | 2232.87 |
49 | 5552.87 | 104.00 | 4447.13 | 33.00 | 2265.87 |
50 | 5448.26 | 104.61 | 4551.74 | 32.39 | 2298.26 |
51 | 5343.05 | 105.22 | 4656.95 | 31.78 | 2330.05 |
52 | 5237.21 | 105.83 | 4762.79 | 31.17 | 2361.21 |
53 | 5130.76 | 106.45 | 4869.24 | 30.55 | 2391.76 |
54 | 5023.69 | 107.07 | 4976.31 | 29.93 | 2421.69 |
55 | 4916.00 | 107.70 | 5084.00 | 29.30 | 2451.00 |
56 | 4807.67 | 108.32 | 5192.33 | 28.68 | 2479.67 |
57 | 4698.72 | 108.96 | 5301.28 | 28.04 | 2507.72 |
58 | 4589.13 | 109.59 | 5410.87 | 27.41 | 2535.13 |
59 | 4478.90 | 110.23 | 5521.10 | 26.77 | 2561.90 |
60 | 4368.03 | 110.87 | 5631.97 | 26.13 | 2588.03 |
61 | 4256.51 | 111.52 | 5743.49 | 25.48 | 2613.51 |
62 | 4144.33 | 112.17 | 5855.67 | 24.83 | 2638.33 |
63 | 4031.51 | 112.82 | 5968.49 | 24.18 | 2662.51 |
64 | 3918.03 | 113.48 | 6081.97 | 23.52 | 2686.03 |
65 | 3803.88 | 114.14 | 6196.12 | 22.86 | 2708.88 |
66 | 3689.07 | 114.81 | 6310.93 | 22.19 | 2731.07 |
67 | 3573.59 | 115.48 | 6426.41 | 21.52 | 2752.59 |
68 | 3457.44 | 116.15 | 6542.56 | 20.85 | 2773.44 |
69 | 3340.61 | 116.83 | 6659.39 | 20.17 | 2793.61 |
70 | 3223.09 | 117.51 | 6776.91 | 19.49 | 2813.09 |
71 | 3104.89 | 118.20 | 6895.11 | 18.80 | 2831.89 |
72 | 2986.01 | 118.89 | 7013.99 | 18.11 | 2850.01 |
73 | 2866.42 | 119.58 | 7133.58 | 17.42 | 2867.42 |
74 | 2746.14 | 120.28 | 7253.86 | 16.72 | 2884.14 |
75 | 2625.16 | 120.98 | 7374.84 | 16.02 | 2900.16 |
76 | 2503.48 | 121.69 | 7496.52 | 15.31 | 2915.48 |
77 | 2381.08 | 122.40 | 7618.92 | 14.60 | 2930.08 |
78 | 2257.97 | 123.11 | 7742.03 | 13.89 | 2943.97 |
79 | 2134.14 | 123.83 | 7865.86 | 13.17 | 2957.14 |
80 | 2009.59 | 124.55 | 7990.41 | 12.45 | 2969.59 |
81 | 1884.31 | 125.28 | 8115.69 | 11.72 | 2981.31 |
82 | 1758.31 | 126.01 | 8241.69 | 10.99 | 2992.31 |
83 | 1631.56 | 126.74 | 8368.44 | 10.26 | 3002.56 |
84 | 1504.08 | 127.48 | 8495.92 | 9.52 | 3012.08 |
85 | 1375.85 | 128.23 | 8624.15 | 8.77 | 3020.85 |
86 | 1246.88 | 128.97 | 8753.12 | 8.03 | 3028.88 |
87 | 1117.15 | 129.73 | 8882.85 | 7.27 | 3036.15 |
88 | 986.67 | 130.48 | 9013.33 | 6.52 | 3042.67 |
89 | 855.43 | 131.24 | 9144.57 | 5.76 | 3048.43 |
90 | 723.42 | 132.01 | 9276.58 | 4.99 | 3053.42 |
91 | 590.64 | 132.78 | 9409.36 | 4.22 | 3057.64 |
92 | 457.08 | 133.55 | 9542.92 | 3.45 | 3061.08 |
93 | 322.75 | 134.33 | 9677.25 | 2.67 | 3063.75 |
94 | 187.63 | 135.12 | 9812.37 | 1.88 | 3065.63 |
95 | 51.72 | 135.91 | 9948.28 | 1.09 | 3066.72 |
96 | 0.00 | 51.72 | 10000.00 | 0.30 | 3067.03 |
Die zur Zeit t bisher insgesamt gezahlten Zinsbeträge (Z_ges):
> t:= 't': Z_ges:= 'Z_ges':
plot({seq(P[i], i = 1..97)},
x = 0..96,
style = point,
symbol = CROSS,
color = red,
labels = [t, Z_ges]);
x = 0..96,
style = point,
symbol = CROSS,
color = red,
labels = [t, Z_ges]);