Clean Price, Dirty Price and Accrued Interest

Identify which price is being discussed

Clean price excludes the accrued coupon component; dirty price includes it. These labels describe a decomposition of value, not different securities. A comparison between a clean quote and a full present value needs an accrual adjustment before any discrepancy can be interpreted. Otherwise, the analyst may report a pricing error that is simply a difference in what the two numbers contain.

FINRA's bond material explains that buyers generally compensate sellers for interest accumulated between coupon payments. The practical implication is to preserve three fields: clean amount, accrued amount and full amount. Do not hide the adjustment in a miscellaneous fee line. Accrued coupon is economically different from commissions or dealer compensation, even when all appear in the final cash settlement.

Treat accrual as a dated convention

For a simple regular coupon period, accrued interest can be expressed as coupon cash multiplied by an elapsed-period fraction. CFA Institute's pricing overview notes that different day-count conventions produce that fraction. The numerator and denominator must come from the same convention. An actual elapsed-day count divided by an unrelated standardized period length is not a neutral approximation unless explicitly justified and labeled.

The relevant date is the settlement basis specified for the calculation, not automatically the date someone looked at a screen. Previous coupon date, next coupon date and entitlement rules also matter. Month-end rules, irregular coupons and ex-coupon arrangements can complicate the familiar identity. A conceptual example can isolate the fraction, but it cannot determine those contract-specific inputs from a coupon rate alone.

Build a hypothetical clean-to-dirty bridge

Assume USD 10,000 face, a 6% annual coupon paid semiannually, and ordinary entitlement to the next coupon. Coupon cash is USD 300. For this arithmetic example only, stipulate that the applicable convention counts 60 elapsed days in a 180-day coupon period. Accrued interest is therefore 300*(60/180) = USD 100. No calendar dates or real security are being inferred.

An assumed clean price of 98.4 per 100 face converts to USD 9,840. Adding USD 100 accrued interest gives a dirty amount of USD 9,940, equivalent to 99.4 per 100 face. This bridge excludes commissions, other charges and taxes. The clean price is an invented input, not a market observation or a valuation produced by the parent calculator.

Understand the coupon-date boundary

Immediately after a scheduled coupon has been paid, the simplified regular-period example resets accrued interest to zero. The remaining bond has lost that coupon receipt, while the holder has received cash. Looking only at the security's full price around the payment can therefore suggest a loss that disappears once the distributed coupon is included in the total-value comparison at the same instant.

The parent model adopts this after-payment boundary and places the next receipt one complete coupon period away. Under that convention, clean and dirty amounts coincide because accrued interest is zero. This is a modeling boundary, not a general statement that every transaction settling on a calendar coupon date has identical operational treatment. Actual entitlement and settlement rules need their own evidence.

Do not attach accrual to an unchanged time grid

Between coupon dates, the next payment is less than a full period away. A full valuation must reflect that shorter discount interval as well as the contractual accrual convention. Adding a guessed accrued amount to a coupon-date result does not generally create a valid between-date price, because the original present-value schedule may still be discounting the next coupon over an entire period.

Similarly, subtracting accrued interest twice can make a clean price appear artificially cheap. Trace which quantity each system returns before reconciling them. If one source already reports a clean amount, a second subtraction is not a conservatism adjustment; it is a duplication. A reconciliation should show the direction of every transformation and retain the original labels so another reader can reverse the bridge.

Keep accrual distinct from investment profit

Paying accrued interest does not buy a separate source of extra yield. Under the ordinary convention, the buyer pays for the seller's elapsed share and later receives the whole next coupon. Treating the entire receipt as newly earned income without considering the accrued amount paid would distort a holding-period calculation. The right cash-flow ledger includes both the initial full outlay and subsequent receipts.

Accounting presentation and tax treatment introduce additional distinctions that this guide does not determine. A cash settlement reconciliation is not a tax opinion or a prescribed bookkeeping entry. Likewise, a clean-price change is not automatically total return. Maintaining separate records for security value, coupon cash and transaction charges makes those later analyses possible without claiming that any one price measure answers them all.

Know when the educational shortcut must stop

FINRA's accrued-interest calculator illustrates that even a focused accrual tool asks which bond category is involved. The parent tool here has no settlement-date or day-count engine, so it cannot reproduce that workflow. Its regular annual, semiannual or quarterly schedule and whole-year maturity inputs are insufficient to establish a real transaction's accrued coupon, cash invoice or entitlement to the next payment.

A sound explanation therefore reports the coupon-date model result separately from any wider settlement illustration. For the hypothetical bridge above, retain the stipulated 60/180 fraction rather than turning it into a purported universal rule. Where actual dates or contract terms are missing, leave the settlement amount unresolved. Precision in a displayed currency total cannot compensate for an undefined accrual convention.

Primary references

1. FINRA: Bonds, including selling between coupon dates
2. CFA Institute: Fixed-Income Bond Valuation: Prices and Yields
3. FINRA: Accrued Interest Calculator