Annuities and level-payment loans
A level-payment loan (a mortgage, a car loan) is an annuity: the same payment every period, part interest and part principal, until the balance is zero. Its payment is PMT = r × PV ÷ [1 − (1 + r)⁻ᵗ], using the periodic rate, the number of payments and the amount actually borrowed.
Watch the lesson 15 min
This lesson's video is for Plus members. The written lesson below is free, as always.
Before this: Pricing bonds: zero-coupon, coupon and perpetual
On the exam
- Calculate and interpret the present value of fixed-income and equity instruments based on expected future cash flows
Calculate and interpret the present value and payment of level-payment (amortizing) instruments. Expect a monthly mortgage payment on the amount financed, a level withdrawal from a lump sum, the present value of an annuity, and how the interest and principal in each payment change.
How deeply to learn each part
- Know the idea
- Understand it in general. It frames other topics, but you will not calculate with it.
- Use it
- Understand it well enough to solve a question with it. Recognize when it applies.
- Memorize
- Learn it by heart. The exam will not give it to you.
You know this one. The full lesson is folded away. The takeaways, formulas and checkpoint below are your quick refresher, and the checkpoint is a fair test of whether you still do.
You tested strong here. The full lesson is folded away. The takeaways, formulas and checkpoint below are your quick refresher, and the checkpoint is a fair test of whether you still know it.
What is an annuity worth?
An annuity pays the same amount every period for a fixed number of periods. In an ordinary annuity the first payment arrives at the end of the first period. Discount each payment and add, or use the closed form for the present value (PV). Call the level payment PMT.
Both calculators normally work in end-of-period mode. Only change the mode when a question says payments come at the start of each period, and change it back afterwards.
How do you find a loan payment?
A level-payment instrument pays the same amount every period, so it is an annuity. A fully repaid amortizing loan , such as a mortgage or a car loan, is the lender’s side of the same picture: the loan amount is the present value, and the payment is the unknown. Turn the formula over.
Use the periodic rate and the number of payments. A monthly loan needs a monthly rate (annual rate ÷ 12) and months (years × 12).
Use the amount you borrow, not the price of what you buy. A home bought for 450,000 with a 20% down payment is financed with a 360,000 loan, and the payment is worked out on the 360,000.
The payment formula is the annuity part of the coupon bond formula from the previous lesson, turned around to solve for the payment.
Exam tip In Excel or Google Sheets, =PMT(0.004, 300, 250000) returns −1,432.49, and =PV(0.07, 10, 5000) returns −35,117.91. Each function has an optional type argument: 0 (the default) for payments at the end of each period, 1 for the start.
An investment pays 5,000.00 at the end of each period for 10 periods. The discount rate is 7.00% per period. Its present value is closest to:
5,000.00 × (1 − 1.07^−10) ÷ 0.07 = 35,117.91
Present value, PV35,117.91
- 2NDCLR TVMwith P/Y set to 1
- 10N7I/Y5000PMT
- CPTPVnegative: it is the money you pay
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PMT payment · CPT compute · PV present value
- fCLEAR FIN
- 10n7i5000PMT
- PVnegative: it is the money you pay
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PMT payment · PV present value
Try this 0 of 3
- Move the year slider to the first year where principal beats interest
- Switch to one payment a year and compare total interest
- Put 20% down and see how much the payment falls
- Interest
- Principal repaid
- Balance
Show working
Periodic rate 4.8% ÷ 12 = 0.4%; payments 25 × 12 = 300.
PMT = r × PV ÷ [1 − (1 + r)−t] = 0.004 × 250,000 ÷ [1 − 1.004−300] = 1,432.49 a month
First payment: interest 250,000 × 0.004 = 1,000.00; principal 1,432.49 − 1,000.00 = 432.49.
Balance after 12 payments = 250,000 × 1.00412 − 1,432.49 × [1.00412 − 1] ÷ 0.004 = 244,694.38
Total paid 300 × 1432.4924 (the unrounded payment) = 429,747.72; minus the 250,000 borrowed leaves 179,747.72 of interest.
- 2NDCLR TVMwith P/Y set to 1
- 300N0.4I/Y250000PV0FV
- CPTPMT−1,432.49
- 12NCPTFV−244,694.38, the balance after 12 payments
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PV present value · FV future value · CPT compute · PMT payment
- fCLEAR FIN
- 300n0.4i250000PV0FV
- PMT−1,432.49
- 12nFV−244,694.38, the balance after 12 payments
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PV present value · FV future value · PMT payment
- Interest only Know the idea interest every period, the whole principal at the end
- Fully amortizing Memorize equal payments that repay interest and principal, balance reaches zero
- Level-payment loan priced as an annuity: mortgage, car loan
-
- Partly amortizing (balloon) Know the idea smaller payments, then a large final payment
How does each payment split between interest and principal?
Each period, interest is the rate times the balance at the start of the period. The rest of the fixed payment repays principal and lowers the balance, so next period’s interest is a little smaller.
The mix moves steadily from interest to principal while the payment never changes.
| Payment | Interest | Principal | Balance after |
|---|---|---|---|
| 1 | 1,000.00 | 432.49 | 249,567.51 |
| 12 | 980.59 | 451.91 | 244,694.38 |
| 150 | 648.52 | 783.97 | 161,345.61 |
| 300 | 5.71 | 1,426.79 | 0.00 |
Exam tip ”What happens to the principal share?” It rises. “What happens to the payment?” Nothing, it is level.
How much can you withdraw from a lump sum?
Use it
An annuity withdrawal turns savings into a level income. It is the same calculation seen from the other side: the lump sum is the present value, and the withdrawal is the payment.
Go deeper Annuity due, interest-only and balloon loans
Not needed for this module’s questions, but it explains the spreadsheet type argument and the calculator’s BGN (begin) mode.
An annuity due pays at the start of each period, so every payment is discounted one period less. Its value is the ordinary-annuity value times (1 + r). The USD 5,000 income stream above would be worth 35,117.91 × 1.07 = 37,576.16 if each payment came at the start of the year.
- 35117.91×1.07= 37,576.16
- 35117.91ENTER1.07× 37,576.16
ENTER enter (on the HP, puts the number on the stack)
Two other loan patterns appear in Fixed Income. An interest-only loan pays interest each period and the whole principal at the end, so it is priced like a bond. A balloon loan amortizes only part of the principal and ends with a large final payment.
Go deeper Why prepayment matters for mortgage pools
A level-payment mortgage is a known stack of cash flows only if the borrower never repays early. Borrowers can repay ahead of schedule, especially when rates fall and they can refinance. That risk shortens the investor’s cash flows at the worst time and is why mortgage-backed securities need their own treatment in Fixed Income.
Memorize this
MemorizeAnnuity formulas
| Want | Formula |
|---|---|
| Present value | |
| Payment | |
| Interest in a payment | opening balance |
| Principal in a payment | interest |
Memory hook The payment formula is the PV formula turned over: PV in, PMT out.
Know it cold Rate and number of payments must match the payment period: monthly loan, monthly rate, monthly count. With a fully amortizing loan, FV = 0. PV is the amount borrowed (or saved), never the full price.
- Interest only Know the idea interest every period, the whole principal at the end
- Fully amortizing Memorize equal payments that repay interest and principal, balance reaches zero
- Level-payment loan priced as an annuity: mortgage, car loan
-
- Partly amortizing (balloon) Know the idea smaller payments, then a large final payment
Quick example
EUR 2,000 at the end of each year for 6 years, discounted at 5%. 2,000 × (1 − 1.05⁻⁶) ÷ 0.05 = EUR 10,151.38.
- 2NDCLR TVM with P/Y set to 1
- 6N5I/Y2000PMT
- CPTPV −10,151.38
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PMT payment · CPT compute · PV present value
- fCLEAR FIN
- 6n5i2000PMT
- PV −10,151.38
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PMT payment · PV present value
Quick example
Borrow 350,000 over 30 years at 4.2% a year, paid monthly. r = 0.35% a month, t = 360. PMT = 1,711.56 a month.
- 2NDCLR TVM
- 360N0.35I/Y350000PV
- CPTPMT −1,711.56
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PV present value · CPT compute · PMT payment
- fCLEAR FIN
- 360n0.35i350000PV
- PMT −1,711.56
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PV present value · PMT payment
Quick example
Balance 250,000 at 0.4% a month, payment 1,432.49. Interest 1,000.00, principal 432.49.
- 250000×0.004= 1,000.00 interest
- +|-+1432.49= 432.49 principal
+|- change sign
- 250000ENTER0.004× 1,000.00 interest
- CHS1432.49+ 432.49 principal
ENTER enter (on the HP, puts the number on the stack) · CHS change sign
How it is asked
-
Monthly mortgage payment
30-year USD 350,000 loan at 4.2%, monthly. Payment?
N = 360, I/Y = 0.35, PV = 350,000, FV = 0, compute PMT: 1,711.56. Interest only (1,225) is the trap.
-
Present value of level payments
EUR 2,000 a year for 6 years at 5%. Value today?
N = 6, I/Y = 5, PMT = 2,000, compute PV: 10,151.38. The undiscounted total (12,000) is the trap.
-
Interest and principal over time
In a level-payment loan, what happens to the principal share of each payment?
It increases, because interest is charged on a shrinking balance.
-
Withdrawal from a lump sum
EUR 600,000 at 4%, equal withdrawals for 25 years. Annual amount?
N = 25, I/Y = 4, PV = −600,000, compute PMT: 38,407.18.
-
Mortgage with a down payment
Home 450,000, 20% down, 30 years at 4.5%, monthly. Which PV?
360,000, the amount financed. Using 450,000 is the trap.
Exam traps
- Using the annual rate and annual periods, then dividing the payment by 12. Convert rate and count to months first.
- Forgetting FV = 0 on a fully amortizing loan. A leftover FV from an earlier problem corrupts the answer.
- Treating the payment as interest only (balance × rate ÷ 12). A level payment also repays principal.
- Computing the payment on the purchase price instead of the amount financed after the down payment.
Checkpoint
3 exam-style questions. About 90 seconds each.
1A borrower takes a 30-year USD 400,000 mortgage at 5.4% a year, paid monthly. The monthly payment is closest to:
2In a level-payment loan, as time passes, the share of each payment that repays principal most likely:
3An investor places GBP 750,000 in an account earning 3.5% a year and plans to withdraw equal amounts at the end of each year for 20 years, leaving nothing at the end. The annual withdrawal is closest to:
Key takeaways
- Level-payment loans are annuities.
- Use the periodic rate and the number of payments.
- Payment fixed, interest share falls, principal share rises.
- Withdrawals from a lump sum are an annuity too: the lump sum is the PV, the withdrawal is the PMT.
Quick example
EUR 2,000 at the end of each year for 6 years, discounted at 5%. 2,000 × (1 − 1.05⁻⁶) ÷ 0.05 = EUR 10,151.38.
- 2NDCLR TVM with P/Y set to 1
- 6N5I/Y2000PMT
- CPTPV −10,151.38
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PMT payment · CPT compute · PV present value
- fCLEAR FIN
- 6n5i2000PMT
- PV −10,151.38
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PMT payment · PV present value
Quick example
Borrow 350,000 over 30 years at 4.2% a year, paid monthly. r = 0.35% a month, t = 360. PMT = 1,711.56 a month.
- 2NDCLR TVM
- 360N0.35I/Y350000PV
- CPTPMT −1,711.56
2ND second function (the shifted label above a key) · CLR TVM clear the time value of money keys · N number of periods · I/Y interest rate per year (per period when P/Y is 1) · PV present value · CPT compute · PMT payment
- fCLEAR FIN
- 360n0.35i350000PV
- PMT −1,711.56
f gold shift key · CLEAR FIN clear the financial registers · n number of periods · i interest rate per period · PV present value · PMT payment
Quick example
Balance 250,000 at 0.4% a month, payment 1,432.49. Interest 1,000.00, principal 432.49.
- 250000×0.004= 1,000.00 interest
- +|-+1432.49= 432.49 principal
+|- change sign
- 250000ENTER0.004× 1,000.00 interest
- CHS1432.49+ 432.49 principal
ENTER enter (on the HP, puts the number on the stack) · CHS change sign
All Quantitative Methods formulas, every lesson
Practice exam-style questions on Time Value of Money in Finance
Questions about this lesson?
Where this comes back
- Fixed-Income Cash Flows and Types Fixed Income
- Mortgage-Backed Securities: RMBS, CMOs and CMBS Fixed Income
Questions candidates ask
How do you calculate a monthly mortgage payment?
Convert to monthly terms: rate ÷ 12 and years × 12. Then PMT = r × PV ÷ [1 − (1 + r)⁻ᵗ], or on the calculator enter N, I/Y and PV with FV = 0 and compute PMT. Use the loan amount after any down payment. A 250,000 loan over 25 years at 4.8% costs 1,432.49 a month.
What is the difference between an annuity and a perpetuity?
An annuity pays a fixed amount each period for a set number of periods, so it ends. A perpetuity pays forever. The annuity formula turns into the perpetuity formula, PMT ÷ r, as the number of periods grows without limit.
How much of a loan payment is interest?
The periodic rate times the balance at the start of the period. On a 250,000 loan at 0.4% a month, the first payment includes 1,000 of interest. The rest repays principal, and the interest share falls every month.
How much can you withdraw each year from a lump sum?
Treat the lump sum as the present value of an annuity and solve for the payment. EUR 600,000 at 4% for 25 years supports equal year-end withdrawals of 38,407.18, leaving nothing at the end.
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