Quick answer
All three are supported. On the engagement details screen set Period end, set Engagement year to first year or continuing, and set Prior period end from last year's accounts. Prior period end is what tells AllDone the period is not twelve months. On a first-year job the incorporation date does the same thing, once it is confirmed.
What each field does
Period end drives the statutory deadlines, calculated on the Companies Act month rule: a month end stays a month end, so a February year end that follows a leap year starts on 1 March and is not pulled back a day.
Prior period end pins the start of this period, and therefore its length, for the accounts and for the corporation tax return.
Trade start date, on a first-year job only, affects the corporation tax computation and the return, not the accounting period. Left blank, AllDone states the assumption it made. A long gap between incorporation and trading is flagged so you can consider dormancy.
Where nothing pins the length, AllDone assumes twelve months and labels the assumption in its output rather than hiding it.
On a first-year job
Last year's signed accounts are not asked for, and the prior-year figures are dropped from the planning questions, because they do not exist. Audit exemption is not concluded at Planning either: the first financial year is tested on its own figures, and those arrive with the records. Planning says so, and the test runs for real at the Working papers step once the figures are in. Anything over the limits is flagged; a figure that is missing is reported as unknown, never counted as a condition met.
Where the period is not twelve months, the note on the exemption test says the annual limits are shown unpro-rated and asks you to confirm the pro-rating.
Payroll and VAT coverage
The number of months AllDone expects to see covered follows the period as entered, so a part-year period asks for part-year payroll and VAT coverage rather than a full twelve months.
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