What is the present value of an annuity, and how do future value and present value annuity tables let you find or back-solve a contribution?
Use future value and present value annuity tables, and calculate the present value of an annuity
The HSC Maths Standard 2 dot point on annuity tables and present value. What the present value of an annuity is, the link PV = FV / (1+r)^n, reading future-value and present-value annuity tables at the period by rate intersection, back-solving a contribution or rate from a table, converting an annual rate to the per-period row, and a loan as the present value of its repayments.
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What this dot point is asking
NESA wants you to do two related things. First, understand and calculate the present value of an annuity: the single lump sum today that is worth exactly the same as a stream of equal future payments. Second, read annuity factor tables. There are two, the future-value-of- table and the present-value-of- table. You find the value where the right period row and rate column meet, then multiply it by the contribution. You also need to back-solve from a table for a required contribution or interest rate. This is the table partner to the future-value formula. The formula gives one answer; the table gives a whole grid of ready-made answers you simply read off.
The answer
Money has a time value. A dollar you will get in three years is worth less than a dollar in your hand today, because today's dollar can be banked to earn interest. The present value of an annuity uses that idea on a whole stream of payments. (An annuity is a series of equal payments made at regular times.) It asks a simple question: if I am promised an equal payment at the end of every period for periods, what single amount today is worth the same? You find the answer by discounting each future payment back to today, that is, working out what it is worth now, and then adding the results. The diagram below does this for four yearly payments of $9000 at . Each future $9000 shrinks as it is pulled back to the present, and the four shrunken amounts add up to a single present value of $31,186.
Present value of a single payment, then of a whole stream
Everything here is built on one rearrangement of the compound interest formula. A lump sum invested now grows to . Make the subject:
This is discounting: dividing a future amount by to find what it is worth today. For example, $10,000 due in years at per annum is worth , i.e. $8638.38 today, because that amount banked now at would grow back to $10,000.
The present value of an annuity just applies this to every payment in the stream and adds them up. If a payment falls at the end of each of periods, the payment periods away is worth today, so
That is a geometric series, a sum where each term is a fixed multiple of the one before. Just as the future-value series folds up into a neat formula, so does this one. You are not expected to add it up by hand in the exam, because the table does it for you. But seeing it as "the sum of each payment discounted back to today" is what makes a table answer make sense, rather than feel like magic.
A loan is the present value of its repayments
The clearest place this idea shows up is a loan. When a bank lends you money today, the amount it hands over is exactly the present value of all the repayments you promise to make. The lender is happy with this, because those future repayments, discounted at the loan rate, are worth exactly what they gave you now. So for a reducing-balance loan (one paid off by equal instalments),
That one sentence lets you back-solve a repayment straight from a present-value table: just divide the amount borrowed by the table factor. It is the same method as a savings goal, only read in the other direction. That is why the present-value table and reducing-balance loans are two views of one idea.
Two tables, one method
There are two annuity tables and they are easy to confuse, so fix the difference firmly.
- The future value of table answers: if I pay in $1 at the end of each period, how much have I accumulated by the end? The factor is . These factors are bigger than (interest has been added on).
- The present value of table answers: a stream of $1 payments at the end of each period is worth how much as a single amount today? The factor is . These factors are smaller than (future money is discounted down).
The procedure is identical for both: find the row for the number of periods, the column for the rate per period, read the factor at the intersection, and multiply by the contribution. The only decision is which table, and that is decided by the word "today" or "now" (present value) versus "after periods", "accumulated" or "final balance" (future value).
Here are small tables for $1, with the factors computed to decimal places. First the future value of $1 at the end of each period:
| Period | ||||||
|---|---|---|---|---|---|---|
And the present value of $1 paid at the end of each period:
| Period | ||||||
|---|---|---|---|---|---|---|
Notice the first row of the future-value table is all : a single payment at the end of period in a -period annuity earns no interest, so $1 paid is $1 accumulated. In the present-value table the first row is the plain one-period discount factor , for example at .
Converting an annual rate to the per-period row
Tables are labelled by the rate and the count per period, not per year. So when interest is added more than once a year (called sub-annual compounding), you must convert before you read the table, exactly as you do with the formula. Divide the yearly rate by the number of compounding periods in a year to get the column. Multiply the number of years by that same number to get the row.
- Yearly contributions, yearly compounding: column , row years.
- Quarterly: column , row years.
- Monthly: column , row years.
So $2000 per quarter for year at per annum compounded quarterly is read at column and row , not at and . Getting this conversion wrong is the most common table error, because the headings tempt you to read the yearly figures straight off.
How exam questions ask about present value and tables
The wording is the whole game. Each phrasing points at one table and one operation. Learn to translate:
- "What single amount today is equivalent to..." or "What lump sum must be invested now to provide..." A present-value question: read the present-value table and multiply, .
- "What will the account be worth after years / at the end of the term?" A future-value question: read the future-value table and multiply.
- "Use the table to find the future value of an annuity of $X..." Straight table read: convert to the per-period row and column, read the factor, multiply by .
- "Find the payment / contribution per period of an annuity whose present value (or future value) is $X." Back-solve: divide the target by the table factor, because means .
- "$A invested at the end of each year for years grows to $B. Find the interest rate." Read across a row: compute the factor you need as , then look along the period- row of the future-value table for the column whose factor matches.
- "How much can be borrowed if the repayment is $R per period..." A loan is the present value of its repayments: amount borrowed . Reverse it to find the repayment from a known loan.
Edge case: which table when the question gives you both numbers
Some questions hand you a future value and ask for a present value, or vice versa, to see whether you discount or accumulate. Anchor on the timeline. If the money you are given sits at the end of the term and you are asked for an equivalent amount now, you are discounting, so use the present-value table (or divide a future value by for a single sum). If you are given regular contributions and asked for the final balance, you are accumulating, so use the future-value table. The two tables are linked: the present value of an annuity grown forward for periods equals its future value, since . In the pension example, $31,185.95 grown at for years gives , which is exactly the future value of the same $9000 annuity, .
Edge case: tables only go so far
A printed table has a fixed set of rows and columns. Sometimes a question needs a rate or a period the table does not list, like a column when the table jumps from to , or period when it stops at . Then the table cannot answer it and you must fall back on the formula. NESA picks table questions so the period and rate you need land on the grid. So if your converted row or column is not in the table, recheck the conversion before assuming you need the formula. The table and the formula always agree where both apply, because the table is just the formula worked out ahead of time for common values.
Exam-style practice questions
Practice questions written in the style of NESA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2021 HSC-style (table-style)3 marksA retiree will draw $9600 at the end of each year for years from a fund earning per annum compounded annually. Using the present-value-of- annuity table, find the single amount that must be in the fund today.Show worked answer →
The present value of the annuity is the lump sum today that is equivalent to the stream of future withdrawals.
Read the present-value-of- table at period , rate : the factor is .
, i.e. $57619.72.
Markers reward selecting the present-value (not future-value) table, reading the correct intersection, multiplying by the contribution, and rounding to cents.
2022 HSC-style (table-style)3 marksAn annuity has a present value of $33240 at per annum compounded annually for years. Using the present-value-of- annuity table, find the payment per period.Show worked answer →
Read the present-value-of- table at period , rate : the factor is .
The present value equals the factor times the payment, so .
Divide: , i.e. about $12435.
Markers reward writing , dividing the target by the table factor, and rounding sensibly.
Practice questions
Original practice questions graded from foundation to exam level, each with a full worked solution. Try them before revealing the solution.
foundation1 marksAn annuity will pay $5000 at the end of each year for years, with money worth per annum compounded annually. Using the present-value-of- annuity table, the factor at period , rate is . Find the present value of the annuity.
Show worked solution →
- Choose the operation
- A present value is wanted from a stream of payments, so multiply the table factor by the payment.
- Use the given factor
- Compounding is annual, so the factor is the one read at period , rate , namely .
- Multiply by the payment
- The present value is the factor times the annual payment.
State the answer. Answer: the present value of the annuity is $13,875.50.
foundation2 marksA retiree will draw a pension of $7500 at the end of each year for years from a fund earning per annum compounded annually. Using the present-value-of- annuity table, find the single amount that must be in the fund today.Show worked solution →
- Choose the table
- The phrase "single amount today" signals present value, so use the present-value-of- table.
- Read the factor at the intersection
- Compounding is annual, so the column is and the row is period . The factor is .
- Multiply by the payment
- The present value is the factor times the annual draw.
State the answer. About $25,988.25 must be in the fund today. Check. Discounting each payment by hand gives , matching the table to a few cents of rounding.
foundation2 marksMia invests $4000 at the end of each year into an account paying per annum compounded annually, for years. Using the future-value-of- annuity table, find the balance at the end of the term.Show worked solution →
- Choose the table
- "Balance at the end of the term" signals future value, so use the future-value-of- table.
- Read the factor
- Compounding is annual, so the column is and the row is period . The factor is .
- Multiply by the contribution
- The future value is the factor times the annual payment.
State the answer. The balance is $13,240.00. Check. The total paid in is , i.e. $12,000.00, so the interest earned is , i.e. $1240.00, which is positive as it must be for an account that earns interest.
foundation2 marksSam pays $6000 into an account at the end of each year for years at per annum compounded annually. Using the future-value-of- annuity table, the factor at period , rate is . Find the balance at the end of the term.
Show worked solution →
- Choose the operation
- A final balance is wanted from regular payments, so multiply the future-value factor by the contribution.
- Use the given factor
- Compounding is annual, so the factor read at period , rate is .
- Multiply by the contribution
- The future value is the factor times the annual payment.
State the answer. Answer: the balance at the end of the term is $12,720.00.
core3 marksA fund must provide a payment of $11\,000 at the end of each year for years to a beneficiary, with the fund earning per annum compounded annually. Using the present-value-of- annuity table, find the single amount needed in the fund today.Show worked solution →
- Choose the table
- The payments fall in the future and a single amount is wanted now, so this is a present value: use the present-value-of- table.
- Read the factor
- Compounding is annual, so the column is and the row is period . The factor is .
- Multiply by the payment
- The present value is the factor times the annual payment.
State the answer. About $43,919.70 is needed in the fund today. Check. The total drawn over the five years is , i.e. $55,000.00, and the present value $43,919.70 is sensibly less than this, because future money is discounted back to today.
core3 marksPriya invests $1500 at the end of each quarter into an account paying per annum compounded quarterly, for year. Using the future-value-of- annuity table, find the balance at the end of the year and the interest earned.Show worked solution →
- Convert to the per-period row and column
- Compounding is quarterly, so the column is and the row is quarters, not column and row .
- Read the factor
- At period , rate , the future-value factor is .
- Multiply by the contribution
- The future value is the factor times the quarterly payment.
Find the interest. The total paid in is , i.e. $6000.00, so the interest is .
State the answer. The balance is $6182.40, including $182.40 of interest. Check. Reading the unconverted row at would give a factor of and a balance of only $1500, which is clearly too small for four deposits, confirming the conversion to row , column was needed.
core3 marksThe Lee family wants $40\,000 in years for a house deposit, saving an equal amount at the end of each year into an account paying per annum compounded annually. Using the future-value-of- annuity table, find the annual contribution required.Show worked solution →
- Set up the table relationship
- The future value equals the future-value factor times the unknown payment, , so to find the payment you divide.
- Read the factor
- Compounding is annual, so the column is and the row is period . The future-value factor is .
- Divide the target by the factor
- Rearranging for gives
State the answer. The family must save about $7095.85 at the end of each year. Check. Multiplying back, , recovering the target, so the division was set up correctly.
core3 marksA retirement fund must pay an equal amount at the end of each year for years to a member, and the fund earns per annum compounded annually. The single amount in the fund today is $25\,000. Using the present-value-of- annuity table, the factor at period , rate is . Find the annual payment the fund can provide.
Show worked solution →
- See the relationship
- The single amount today is the present value of the payment stream, so , and the payment is found by dividing.
- Use the given factor
- Compounding is annual, so the present-value factor is the one at period , rate , namely .
- Divide the present value by the factor
- Rearranging for the payment gives
State the answer. Answer: the fund can pay about $5740.13 at the end of each year. Check. Multiplying back, , recovering the present value, so the division was set up correctly.
exam4 marksJordan borrows $28\,000 for a car at per annum compounded annually and repays it in equal instalments at the end of each year for years. Using the present-value-of- annuity table, find the annual repayment, and hence the total interest paid over the life of the loan.Show worked solution →
- See the loan as a present value
- The amount borrowed is the present value of the repayment stream, so , and the repayment is found by dividing.
- Read the factor
- Compounding is annual, so the column is and the row is period . The present-value-of- factor is .
- Divide the loan by the factor
- Rearranging for the repayment gives
Find the total interest. Over years the total repaid is , i.e. about $34,165.08, so the interest is , about $6165.08.
State the answer. Jordan repays about $5694.18 at the end of each year, paying about $6165.08 in interest in total. (Using the unrounded factor gives a repayment of about $5694.15; the few cents difference is table rounding.) Check. The total repaid $34,165.08 exceeds the $28,000 borrowed, as it must for a loan that charges interest.
exam3 marksAn annuity of $12\,500 invested at the end of each year for years grows to a future value of $40\,580. Using the future-value-of- annuity table, find the annual interest rate.Show worked solution →
Compute the factor you need. Since , the required factor is the future value divided by the contribution.
- Match the factor along the period- row
- Scan the row for period in the future-value table for the column whose factor is . The column is , the column is , and the column is .
- Read off the rate
- The exact match is the column.
- State the answer
- The annuity earns per annum. Check. Reading forwards at , , which is the given future value, confirming the rate.
exam4 marksAn annuity has a present value of $30\,000 at per annum compounded annually for years. Using the present-value-of- annuity table, find the payment per period.Show worked solution →
- Identify the table and operation
- A present value is given and the payment is wanted, so use the present-value-of- table and back-solve, since means you divide.
- Read the factor
- Compounding is annual, so the column is and the row is period . The present-value-of- factor is .
- Divide the present value by the factor
- Rearranging for the payment gives
State the answer. The payment per period is about $9877.19. Check. Multiplying back, , recovering the present value, so the back-solve was set up correctly.
exam5 marksAisha saves $3000 at the end of each year for years into an account paying per annum compounded annually. From the annuity tables, the future-value-of- factor at period , rate is , and the present-value-of- factor at the same intersection is . (a) Find the balance at the end of the years and the total interest earned. (b) Find the single amount Aisha could instead invest today to provide the same future balance, and confirm it is the present value of the annuity.
Show worked solution →
Part (a): choose the future-value table. A final balance from regular savings means future value, so multiply the future-value factor by the contribution.
The total paid in is , i.e. $15,000.00, so the interest earned is .
Part (a) answer. The balance is $17,599.80, including $2599.80 of interest.
Part (b): use the present-value table. The lump sum today equivalent to the same stream is the present value of the annuity, found by multiplying the present-value factor by the payment.
Confirm the link. Growing this present value forward for years gives , matching the balance in part (a) to a few cents of table rounding, so it is indeed the present value of the annuity.
Part (b) answer. Answer: (a) the balance is $17,599.80 with $2599.80 interest; (b) the equivalent single amount today is $11,978.10, the present value of the annuity.
Related dot points
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