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Introduction to Finance

Streams of payments, priced in one number.

Perpetuities, annuities and loans are just many payments brought back to today. Learn the shortcuts, then the rate traps: APR or EAR, which period, and real or nominal.

Part 1 · Perpetuities · Step 1 of 13

A stream of payments: bring each one back on its own

A client pays a studio four amounts, years 1 to 4
010k20k30kdollars$3.7kYear 1÷ 1.08¹$5.1kYear 2÷ 1.08²$2kYear 3÷ 1.08³$7.4kYear 4÷ 1.08⁴$22.5k$18.2kTotaladded up
as paidworth today
From the time value of money tool: money moves forward with FV = C(1 + r)T and back with PV = C ÷ (1 + r)T. A stream of uneven payments is just several single payments. Bring each one back to today with its own number of years, then add. That is value additivity. Adding the payments as they are paid mixes dollars from different years, which are not the same thing.
Try it: Move the rate from 1% to 20%. Later payments have a larger percentage change in value. Their dollar change also depends on the payment amount.
Interest rate, r8%
Year 4 payment$10,000
YearPaidDivide byWorth today
1$4,000.001.081$3,703.70
2$6,000.001.082$5,144.03
3$2,500.001.083$1,984.58
4$10,000.001.084$7,350.30
Total$22,500.00$18,182.62
Added as paid, the stream looks like $22,500.00. Its value today is $18,182.62. The gap, $4,317.38, is the interest you could earn on today's money while you wait for the later payments.
Check yourself
True, false or uncertain: the present value of a positive future cash receipt at a fixed date rises when its discount rate falls.

Midterm coming up and annuities still feel slippery?

Bring your problem sets. We work through them together until every type feels routine.

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