What it means
True interest cost is a way to compare borrowing offers when cash arrives and leaves at different times: an issuer receives proceeds at sale and pays interest and principal over future dates, and TIC is the discount rate that balances these cash flows in present-value terms. The calculation is used particularly in competitive municipal bond bidding.
A lower coupon is not necessarily a lower cost, because a bidder might offer a bond at a discount, giving the issuer less cash now for similar future payments, while another bid may include a premium, and comparing only the stated interest rate misses those differences in proceeds and timing. The Municipal Securities Rulemaking Board's Rule G-33 covers specified municipal security calculations, including yield conventions, and for a particular sale the issuer's notice and bid documents define how bids are compared.
TIC terminology can vary with the market and contract, so read the actual bid terms rather than applying a generic online calculator uncritically. To calculate a rate, list the issuer's net proceeds and each scheduled debt-service payment, choose a discount rate, discount each future payment to the sale date and add those present values, then adjust the rate until the sum equals the relevant proceeds under the bid rules.
Spreadsheets solve this iteratively, because there is not usually a simple add-and-divide formula. A basic illustration shows why timing matters: borrow 100 today and repay 110 one year later and the simple one-period rate is 10% if there are no other flows, but pay a 5 upfront fee and receive only 95 while still repaying 110 and the effective one-year cost rises to about 15.79%, although real bond schedules are more complex.
Do not call every loan's annual percentage rate "TIC." Consumer-credit APR is usually governed by local disclosure rules and may include different charges or conventions, and effective interest under financial reporting has its own recognition and measurement purposes. These measures are related through discounted cash flows but need not produce the same quoted figure.
Issue expenses can affect the issuer's economic cost, since underwriting charges, legal fees and other sale costs reduce usable proceeds depending on the comparison method, and some bid evaluations may exclude certain costs that are common to every bid, so keep a second all-in financing view so the budget reflects what the issuer actually receives and pays. TIC helps rank offers on a common time-value basis, but it is not a complete credit or risk analysis, because a bid may have legal conditions, redemption provisions or execution risks and a fixed-rate schedule has different future flexibility from a variable-rate loan.
Read these terms alongside the calculation. Compare the cash that can be used: if 10 million of face value produces 9.7 million in net proceeds, the issuer cannot fund a 10 million project without another source, and the repayment schedule belongs against the relevant net proceeds, not the bond's face amount merely because it is printed on the certificate.
Review the result with finance advisers before accepting a material issue by reconciling the inputs to the bid, confirming fee treatment, checking that the selected bid meets formal criteria and keeping the calculation workbook and bid documents together, since a small formula error on a long repayment schedule can alter a decision. TIC is a useful comparison tool because it gives future payments weight according to when they occur, but it does not tell whether the borrower can afford those payments or whether the project should be funded, so pair the rate with cash-flow forecasts, covenants, total debt service and alternatives, and then the number informs a decision rather than replacing it.
In practice
Real-world examples.
Example
A 6% coupon with an upfront issuer fee can have a higher present-value borrowing cost.
Example
An issuer compares two competitive municipal bond bids using the prescribed TIC method.
Example
Monthly repayments raise the effective cost compared with annual.
Formula
Calculation
TIC is the rate r such that net proceeds equal the present value of all scheduled debt-service payments, each discounted by its payment date.
Illustrative annual-payments example: net proceeds $980,000 after a $20,000 fee; pay $60,000 interest annually for three years and repay $1,000,000 principal with the last coupon. Solving $980,000 = $60,000/(1+r) + $60,000/(1+r)^2 + $1,060,000/(1+r)^3 gives r about 6.76%.
A check shows the answer is sensible. At the 6% coupon rate the same payments would be worth exactly $1,000,000, so receiving only $980,000 must push the rate above 6%. Discounting at 6.76% gives about $56,200 + $52,600 + $871,200 = about $980,000, which matches the net proceeds.Case study
Seen in the real world.
This illustrative and entirely fictional case follows Bay City Water Board, an invented issuer comparing two bond bids. One bid offers a lower coupon but less money up front. Its advisers calculate TIC for both using the stated payment dates and net proceeds, then consider other bid conditions. The apparent low coupon need not be the cheaper financing.
Watch out
Common mistakes.
- Comparing headline rates only.
- Ignoring fees.
- Ignoring payment timing.
Questions
People also ask.
What is true interest cost?
The real annual cost of borrowing, including fees and timing.
How is it different from the headline rate?
It includes fees and uses the time value of money.
Where is it used?
Comparing competitive bond bids; related discounted-cash-flow methods can inform loan comparisons.
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