Total Return Attribution for Bond Portfolios

A bond portfolio manager reports a 2.1% quarterly return. That single number hides a question every allocator eventually asks: was that return earned by correctly calling the direction of interest rates, by picking the right credits, or would the portfolio have made almost the same money sitting still and simply collecting coupons? Total return attribution answers that by splitting the return into its component sources.

The standard building blocks

Carry is the return earned just from holding the bonds and collecting coupons, assuming nothing else changes. Rolldown is the price gain from a bond "rolling down" an upward-sloping yield curve as time passes and it becomes a shorter-maturity bond, which (holding the curve shape fixed) typically has a lower yield and hence a higher price. Together these are the return a passive, unchanged position earns purely from time passing — no view required. The remainder of the return is active: a rates effect (how much the portfolio's duration exposure gained or lost from the level of yields moving) and a spread effect (how much overweighting certain credits versus the benchmark added or subtracted as spreads moved).

Worked example

A corporate bond portfolio returns 2.10% over a quarter. Decomposing it:

1. Carry. The portfolio's average coupon over the quarter, roughly 4.20% annualized, contributes about $4.20\% / 4 = 1.05\%$ for the quarter.
2. Rolldown. As bonds age down a steep part of the curve, this adds another 0.25% for the quarter, estimated by comparing the bond's actual price change to what pure time-decay along a static curve would predict.
3. Rate effect. Benchmark yields fell 15 basis points during the quarter; with portfolio duration of about 6, that contributes roughly $6 \times 0.15\% = 0.90\%$.
4. Spread effect. The remainder, $2.10\% - 1.05\% - 0.25\% - 0.90\% = -0.10\%$, is attributed to credit spreads — the portfolio's credit overweights slightly underperformed as spreads on its specific holdings widened a touch more than the benchmark's.

This tells the manager: income and the falling-rate environment did the heavy lifting, and the active credit selection call actually cost a small amount this quarter — a very different story than the headline 2.10% alone would suggest.

What this means in practice

Allocators use attribution to judge whether a manager's stated skill (say, "we add value through credit selection") shows up where it's claimed — a manager who claims credit expertise but whose returns are attribution-explained almost entirely by carry and rate bets isn't demonstrating the skill they're being paid for. Risk teams use the same decomposition prospectively, budgeting how much expected return should come from carry versus active positioning, so that a quarter's performance can be judged against what was actually intended rather than just the total number.