There is no point reaching for a calculator that cannot show its working. This one starts from annual coupon rate, coupon frequency, face value, years to maturity, yield differential, yield to maturity (ytm) and one way and reports downwards bond price, upwards bond price and effective duration, so you can see how each answer follows from the numbers you entered.
What Is the Effective Duration Calculator?
The effective duration calculator takes annual coupon rate, coupon frequency, face value, years to maturity, yield differential, yield to maturity (ytm) and one way and turns them into downwards bond price, upwards bond price and effective duration.
It is the kind of calculation you would otherwise do on the back of an envelope: mechanical, repeatable and easy to get subtly wrong without noticing.
How the Effective Duration Figure Is Built
Each result is calculated from the ones before it, so the working is fully visible. That matters when the answer is going to be quoted to somebody else and you need to be able to explain where it came from.
The figures are exactly as good as the assumptions underneath them. Check the rates, the periods and the tax treatment before you rely on the result.
Reading the Result Sensibly
A small change in an input can move the result by much more than you would expect, particularly where the calculation divides by one of the figures you supplied. That is worth understanding before you rely on a figure.
For anything that will be committed to, write the inputs down beside the result. A number you can reproduce is worth far more than one you cannot explain.
A Worked Example
Working through an example, with annual coupon rate set to 10, coupon frequency set to 1.000000000000000, face value set to 5, the calculator returns bond price of 5, and coupon per period of 50, and annual coupon of 50. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out downwards bond price?
Enter annual coupon rate, coupon frequency, face value, years to maturity, yield differential, yield to maturity (ytm) and one way. The calculator then works through the relationship and reports downwards bond price, upwards bond price and effective duration.
What does the effective duration actually calculate?
It takes annual coupon rate, coupon frequency, face value, years to maturity, yield differential, yield to maturity (ytm) and one way and converts them into downwards bond price, upwards bond price and effective duration using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter annual coupon rate?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.