Mortgage

Monthly payment at per yearly percent for N payments of T1 amount loaned

pay[T1_, N_, per_] := (per/12 (1 + per/12)^NT1)/((1 + per/12)^N - 1)

Amount owed after n payments

Tn[n_, T1_, N_, per_] := ((1 + per/12)^n - (1 + per/12)^N ((1 + per/12)^n - 1)/((1 + per/12)^N - 1)) T1

Total interest payed after N payments

Itotal[T1_, N_, per_] := N pay[T1, N, per] - T1

Monthly payments for a car ($24 000) for 60 months at 3,9% vs 5.9% and total interest paid after 60 months

pay[24500,60,0.039]
pay[24500,60,0.059]
Itotal[24500,60,.039]
Itotal[24500,60,.059]

450.1

472.515

2506.

3850.92

Monthly payment on $160,000 at 5.8% over 15, 14 and 10 years

pay[160000, 180, 0.068]

pay[160000, 168, 0.058]

pay[160000, 120, 0.058]

1420.29

1392.99

1760.3

Amount owed after 12 months

t13180 = Tn[12, 160000, 180, 0.058]

t13168 = Tn[12, 160000, 168, 0.058]

t13120 = Tn[12, 160000, 120, 0.058]

153103.

152363.

147836.

t13180 - t13168

739.998

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