diff --git a/hledger-lib/hledger_journal.m4.md b/hledger-lib/hledger_journal.m4.md
index 714604309..cc16f91b1 100644
--- a/hledger-lib/hledger_journal.m4.md
+++ b/hledger-lib/hledger_journal.m4.md
@@ -1402,23 +1402,26 @@ So,
 
 ### Forecasting with periodic transactions
 
-With the `--forecast` flag, each periodic transaction rule generates
-future transactions recurring at the specified interval.
-These are not saved in the journal, but appear in all reports.
-They will look like normal transactions, but with an extra
-[tag](journal.html#tags):
+The `--forecast` flag activates any periodic transaction rules in the journal.
+They will generate temporary recurring transactions,
+which are not saved in the journal, but will appear in all reports
+(eg [print](hledger.html#print)).
+This can be useful for estimating balances into the future,
+or experimenting with different scenarios.
+Or, it can be used as a data entry aid: describe recurring
+transactions, and every so often copy the output of `print --forecast`
+into the journal.
 
-- `generated-transaction:~ PERIODICEXPR`  - shows that this was generated by a periodic transaction rule, and the period
+These transactions will have an extra [tag](journal.html#tags)
+indicating which periodic rule generated them:
+`generated-transaction:~ PERIODICEXPR`.
+And a similar, hidden tag (beginning with an underscore) which,
+because it's never displayed by print, can be used to match
+transactions generated "just now":
+`_generated-transaction:~ PERIODICEXPR`.
 
-There is also a hidden tag, with an underscore prefix, which does not appear in hledger's output:
-
-- `_generated-transaction:~ PERIODICEXPR`
-
-This can be used to match transactions generated "just now",
-rather than generated in the past and saved to the journal.
-
-Forecast transactions start on the first occurrence, and end on the last occurrence,
-of their interval within the forecast period. The default forecast period:
+Periodic transactions are generated within some forecast period.
+By default, this
 
 - begins on the later of
   - the report start date if specified with -b/-p/date:
@@ -1426,25 +1429,23 @@ of their interval within the forecast period. The default forecast period:
     or today if there are no normal transactions.
 
 - ends on the report end date if specified with -e/-p/date:,
-  or 180 days from today.
+  or 6 months (180 days) from today.
 
-where "today" means the current date at report time.
-The "later of" rule ensures that by default forecast transactions do not overlap normal transactions in time;
-they will begin only after normal transactions end. If you wish to use your own forecast period,
-you can provied it via `--forecast=PERIODICEXPR`.
+This means that periodic transactions will begin only after the latest
+recorded transaction. And a recorded transaction dated in the future can
+prevent generation of periodic transactions.
+(You can avoid that by writing the future transaction as a one-time
+periodic rule instead - put tilde before the date, eg `~ YYYY-MM-DD ...`).
 
-Forecasting can be useful for estimating balances into the future,
-and experimenting with different scenarios.
-Note the start date logic means that forecasted transactions are automatically replaced
-by normal transactions as you add those.
-
-Forecasting can also help with data entry:
-describe most of your transactions with periodic rules,
-and every so often copy the output of `print --forecast` to the journal.
-
-You can generate one-time transactions too:
-just write a period expression specifying a date with no report interval.
-(You could also write a normal transaction with a future date, but remember this disables forecast transactions on previous dates.)
+Or, you can set your own arbitrary "forecast period", which can
+overlap recorded transactions, and need not be in the future, by
+providing an option argument, like `--forecast=PERIODEXPR`.
+Note the equals sign is required, a space won't work.
+PERIODEXPR is a [period expression](hledger.html#period-expressions),
+which can specify the start date, end date, or both,
+like in a [`date:` query](hledger.html#queries).
+(See also hledger.1 -> [Report start & end date](hledger.html#report-start-end-date)).
+Some examples: `--forecast=202001-202004`, `--forecast=jan-`, `--forecast=2020`.
 
 ### Budgeting with periodic transactions