Interest

Simple Interest
r is annual rate as a decimal
P is principle
n is number of years
A is present value
A = P(1+nr)

Compound Interest
Interest compounded annually
A = P(1+r)ᴺ
r is annual rate as a decimal
P is principle
N is number of years
A is present value

Interest compounded biannually
A = P(1+(r/2))^(2n)
r is annual rate as a decimal
P is principle
n is number of years
A is present value

Interest compounded quarterly
A = P(1+(r/4))^(4n)
r is annual rate as a decimal
P is principle
n is number of years
A is present value

Interest compounded monthly
A = P(1+(r/12))^(12n)
r is annual rate as a decimal
P is principle
n is number of years
A is present value

Interest compounded daily
A = P(1+(r/365))^(365n)
r is annual rate as a decimal
P is principle
n is number of years
A is present value

Interest compounded continuously
A = Pe^rt
e = 2.718282
r is annual rate as a decimal
P is principle
A is present value
t is loan period in years

Mortgage payment
A = Pr / (1 – (1 + r)⁻ⁿ)
 A  is the periodic amortization payment
 P  is the principal amount borrowed
 r  is the percentage rate per period; for a monthly payment,
     take the Annual Percentage Rate (APR)/12
 n  is the number of payments; for monthly payments over 30 years,
     12 months x 30 years = 360 payments.