IRR since inception is the annual rate that makes the present value of every cash flow in and out of a portfolio — buys, coupons, sales and the current value — come to zero, so it measures the return on the money actually committed rather than on a unit of the portfolio.
A rate that fits the actual cash flows
The portfolio view carries a figure it labels IRR since inception, and it means exactly that: the internal rate of return of every cash flow in and out of the portfolio, from the first one up to the report date. The flows are the money you actually committed and received — each purchase, each sale and redemption, each coupon — and the final flow is the portfolio's market value at the report date, treated as though the positions were all realised then. The IRR since inception is the single annual rate that discounts all of them to a present value of zero.
That definition is why it is called money-weighted. It is not the return of a unit of the portfolio over time, which ignores how much money was invested when; it is the return on the pounds, so a large purchase made just before a good run counts for more than a small one made before a bad one. Two people holding the same gilts can have different IRR figures because they put their money in at different moments.
Worked once
The table below runs the simplest possible portfolio through the arithmetic. It is illustrative — round numbers, not from any portfolio or report — and the flows fall on just two dates, which lets the rate be solved directly rather than iteratively. A single gilt is bought for £9,800 and, one year later, a £200 coupon has been received and the position is valued at £10,188.
| Date | Flow | Amount | Direction |
| 2025-10-15 | Buy £10,000 nominal at a dirty price of 98.00 | £9,800.00 | out |
| 2026-10-15 | Coupon received on the anniversary | £200.00 | in |
| 2026-10-15 | Closing market value at the report | £10,188.00 | in |
Everything that comes in on the second date is £200 + £10,188 = £10,388. The rate that discounts £10,388 in a year and £9,800 at the start to zero is the rate at which £10,388 ÷ (1 + r) = £9,800, so 1 + r = 10,388 ÷ 9,800 = 1.06, and r = 6.00 per cent. With flows on more dates the same equation holds — the present value of every flow, discounted at r by its own time to the report date, sums to zero — and the page solves for the r that makes it so, because there is no closed-form solution once the flows are irregular.
What the closing value is and is not
The IRR since inception treats the current market value of the portfolio as a final inflow at the report date. That is a convention, not a sale: the money has not been realised, and the figure is a mark-to-market rate, so it moves with the portfolio's value on the day. If a position is sold, its proceeds enter the flows as a real inflow and the market value afterwards no longer includes it, so the rate is not changed by selling, only by the price at which it is sold.
- Purchases are outflows: money committed to the portfolio.
- Coupons are inflows: income received along the way.
- Sales and redemptions are inflows: principal and gain returned.
- The closing market value is an inflow by convention: what the holdings are worth at the report date.
- A figure that says nothing about timing would not be an IRR; the dates of the flows are the whole of it.
When there is no honest figure
An IRR needs cash flows it can bracket: at least one outflow and one inflow, on at least two dates. A portfolio with no holdings at or before the report date has nothing to solve; one with a single flow date has no rate to find; and one whose flows never change sign has no root at which to set the present value to zero. In each of those cases the site shows an em dash rather than a rate, because a made-up 0.00 per cent would be worse than an absent figure. The em dash is the honest cell.
IRR is not realised P&L
The two figures answer different questions and are easy to confuse. Realised P&L is the gain or loss already booked on positions that have been sold or redeemed — it is money settled, a pound figure, and it ignores what is still held. The IRR since inception is a rate over the whole portfolio, holdings included, and it is money-weighted. A portfolio can show a healthy IRR on the strength of a rise in prices that has not been realised, and a modest realised P&L from a few sales; neither contradicts the other. The attribution tab on a gilt's own page, reached from the conventional gilts list, is a third question again — how a single held position's return was made up — and it is not an IRR either.
Background, not advice
This explains what IRR since inception measures, how the actual cash flows build it, and when the site declines to show one; it is general background, not investment, tax or legal advice for any reader's circumstances. The figures above are illustrative, and a real IRR since inception is computed from the trades booked in the portfolio and marked at the day's report. An IRR that moves with the closing value is a rate on a valuation, not a promise about the future.