A ladder does not always pay an identical amount every year — an empty rung, declining coupons or a target that rises faster than the cash can leave a year short — and the projection shows which years miss the target and by how much.
What a shortfall year is
A shortfall year is a year in which a ladder's income misses the target it was designed to pay. The target in income target mode is the reader's chosen income, uplifted each year at the inflation assumption, so the amount owed rises across the window. A shortfall is any year where the rungs fail to fund that year's draw — whether entirely, because no rung resolved for the year, or partly, because the cash that arrived fell below the uplifted target. Reading a ladder year by year, rather than trusting a single total, is what makes a shortfall visible.
Why shortfall years happen
There are two distinct causes, and they behave differently. The first is an empty rung: a year band in which no conventional gilt matures nearby, so no rung is built and that year's draw has nothing funding it. The whole target for that year is a shortfall. The second is a mismatch of shape: the target rises each year with the inflation assumption, while a ladder's coupon income falls as rungs mature and stop paying, so a reader who counts coupon income rather than the redemption-funded draw can find later years looking short even though the draw itself is funded.
- An empty rung leaves a whole year's draw unfunded.
- Coupon income declines as rungs mature, so coupon-only reading understates later years.
- The target rises each year, so a flat cash flow falls behind it over time.
- Both causes show in the per-year projection, which a single total hides.
Reading the projection for a gap
The rungs-by-years projection on the bond ladder designer is where a shortfall is read. Each rung's coupon shows in every year it runs, and an em dash marks the years after it has matured. The column totals down the page are the year's income, and comparing each column against that year's uplifted target is what reveals a gap: a column below its target is a shortfall year, and a column that is empty altogether is an empty rung. The projection does not model part-year coupons or the final accrued amount, so it is a shape rather than a schedule, but it is enough to see which years fall short.
A shortfall year worked through
The table is an illustration and not a quote from any gilt. It takes a £10,000 first-year target uplifted at 3 per cent a year across a five-year window, with the fourth year marked as an empty rung to show a full shortfall, and prices each rung at par. The £10,000, the 3 per cent and the empty fourth year are illustrative inputs; the uplift arithmetic is exact.
| Year | Target draw (uplifted at 3%) | Rung this year | Draw funded | Shortfall |
| 1 | £10,000.00 | Yes | £10,000.00 | £0.00 |
| 2 | £10,300.00 | Yes | £10,300.00 | £0.00 |
| 3 | £10,609.00 | Yes | £10,609.00 | £0.00 |
| 4 | £10,927.27 | No — empty rung | £0.00 | £10,927.27 |
| 5 | £11,255.09 | Yes | £11,255.09 | £0.00 |
Years one, two, three and five are funded to their targets because each has a rung sized to its uplifted draw. Year four has no rung, so its whole £10,927.27 target is unmet — the clearest kind of shortfall year. The remaining rungs still fund their own years; the empty year simply has nothing behind it. A partially funded year would show a smaller gap in the same column: a draw above the cash that arrived, but not above zero.
What a shortfall year means, and the options it opens
A shortfall is information, not a verdict. Seeing a gap lets a reader weigh what to change, and the page offers several levers without prescribing any. Lengthening or shortening the window changes which years are covered; a nearer band may resolve where a distant one did not. Filling the empty year with the nearest still-running gilt — the page already does this where a candidate qualifies — can close a gap, at the cost of a rung whose maturity is off its band. An index-linked or mixed ladder changes the shape again. Or a reader may accept the gap and meet that year from elsewhere. The page states what each set of inputs produces; the choice of which to adjust is the reader's.
It also helps to check the target against the cash the ladder actually generates. The coupon calendar shows the dated coupons and redemptions that land across the gilts a reader holds, so a projection's shortfall year can be set against the real payment dates. Where the projection shows a gap, the calendar shows whether any real payment falls in that year and how large it is.
Background, not advice
This article explains what an income shortfall year is in a ladder, why one arises, and how the projection shows it. It is general background on how the figures are put together, not investment, tax or legal advice for any reader's circumstances, and nothing here says what a reader ought to do about a gap. The illustration prices every rung at par and states its inputs, and the projection is an idealised shape rather than a schedule. The primary source for a real gilt's maturity, coupon and payment dates is the gilt's own record and the Debt Management Office.