Each gilt carries its own daily yield change, and across a portfolio those changes differ — the spread between them, multiplied by each holding's modified duration, is what actually moves a portfolio's value from one report to the next.
The change is a per-gilt figure
The site records a yield change against each gilt: how far its yield has moved since the previous close. It sits beside the gilt on the lists, as a small change cell next to the yield, and it is the same figure behind the key-rate cells on the gilt yield curve when the comparison period is the previous day. It is a quoted change in yield, not a change in price, though for a fixed-coupon gilt the two run in opposite directions: a rising yield is a falling price.
The change is stamped by the report rather than solved on the page: each day's report compares a gilt's yield with the previous stored close, so the figure on a list is the move between two reports. A gilt the pipeline could not price on both days has no change to show, which is why the cell can read blank rather than zero — an absent change is not the same as no change.
Across a portfolio it is a spread
A portfolio holds several gilts, and on any given day each of them has its own yield change. They are rarely equal. The short end can move more than the long end, or less, and the result is a spread of changes across the holdings rather than one number for the whole portfolio. Reading the spread is the first step to understanding why a portfolio's value moved the way it did, because the portfolio's move is not the market's single move but the sum of its holdings' different ones.
Duration turns each change into pounds
A yield change on its own says nothing about money; it has to be scaled by the holding. That is what modified duration and the DV01 do. The DV01 of a holding is the modified duration times the market value divided by ten thousand, which gives the money value of one basis point of yield on that holding; multiplied by the holding's own daily yield change, it gives an approximate money move for the day. The table below runs three illustrative holdings through it. The figures are round numbers chosen to show the point and are not from any gilt or report.
| Holding | Market value | Modified duration | Daily yield change | DV01 | Approx. value change |
| X | £9,800 | 3.0 years | −10 bp | £2.94 | −£29.40 |
| Y | £12,000 | 12.0 years | +2 bp | £14.40 | +£28.80 |
| Z | £4,900 | 8.0 years | −6 bp | £3.92 | −£23.52 |
| Total | £26,700 | — | spread 12 bp | — | −£24.12 |
Holding Y's yield barely moved — two basis points — but because its modified duration is twelve years its money move is almost as large as holding X's, whose yield fell ten basis points on a much shorter duration. That is the lesson the spread teaches: a small change on a long holding can matter as much in money as a large change on a short one, and the portfolio's daily move is the net of all of them.
The DV01 is fixed for the day — the modified duration times the market value at the report's price — so the only thing that varies across the holdings is each one's daily yield change. That is why the spread, more than the duration, is what makes one day move a portfolio further than the next.
What the spread itself says
When every holding's yield change is roughly the same, the curve has shifted in parallel and the portfolio's move is close to what a single duration figure would predict. When the changes pull apart — the short end down while the long end is up, say — the curve has changed shape, and each holding has moved by its own amount rather than a common one. The spread is the record of that reshaping.
The portfolio's own numbers make the point concrete. Each holding carries a market yield and a modified duration on the portfolio view, and the daily change is what connects the two to a money move. Two portfolios with the same total duration can have moved by different amounts on the same day because their holdings sit at different points on the curve and those points moved differently.
A single duration number describes the response to a parallel move. The daily yield change per holding is what shows whether the move was parallel at all.
It is worth reading the spread as a description rather than a signal. A wide spread is not a warning and a narrow one is not a comfort; both are statements about how the curve moved that day. The portfolio view shows each holding's market yield and modified duration side by side, so the spread can be read against the durations that scale it into money.
Background, not advice
This explains how a per-gilt daily yield change becomes a spread across a portfolio's holdings, and how duration turns each change into a money move; it is general background, not investment, tax or legal advice for any reader's circumstances. The figures above are illustrative, and the authoritative yield change and modified duration for any gilt are the ones the site computes for the day's report. A yield change is a record of the last move, not a forecast of the next.