Carry-over rules
What happens to leftover money — and leftover deficits — when the month ends.
Carry-over is what happens at midnight on the last day of a month. Project Budget runs one short rule for every category. The rule is asymmetric: surplus rolls; deficit doesn't.
The rule, in one paragraph
If a category's Available at month-end is positive, that amount becomes the carry-in for the same category next month. If Available is negative, the carry-in resets to zero and the deficit is subtracted from next month's Ready to Assign. If Available is exactly zero, nothing happens.
Why surplus rolls
Because the envelope still has money in it. If you assigned $400 to Groceries and only spent $350, the remaining $50 doesn't vanish — it's groceries money you didn't need yet. Next month starts with $50 already in the envelope; whatever you assign on top of that is additive.
This is what makes True Expenses work. You can assign $50/month toward Car insurance for six months, watch the balance grow to $300, and pay the semi-annual bill from accumulated dollars without disrupting any other category.
Why deficit resets
If Groceries ends the month at -$23 (you spent $23 more than was in the envelope), Project Budget does not start next month at -$23. The reasons are practical:
- A perpetual hole compounds month over month and becomes psychologically defeating.
- The dollars came from somewhere real — your accounts. That "somewhere" was Ready to Assign, drawn against your future income.
- The honest accounting is: you spent $23 that hadn't been assigned to anything yet. Next month's RTA absorbs the hit and the category starts fresh.
Worked example
Two-month run of Groceries:
| Month | Carry-in | Assigned | Activity | Available | Carry-out → next month |
|---|---|---|---|---|---|
| April | $0 | $400 | -$350 | $50 | $50 carries in to May |
| May | $50 | $400 | -$480 | -$30 | $0 carry-in to June; RTA reduced by $30 on June 1 |
By June 1, Groceries shows $0 carry-in. You assign fresh from a Ready to Assign that's $30 lighter than it would have been.
Credit-card categories carry too
The Credit Card Payment category follows the same surplus-rolls / deficit-resets rule. In practice it rarely ends a month negative — that would mean you paid more than the card owed, which is unusual.
Tracking-account "categories"
Tracking accounts don't have categories and don't participate in carry-over. Their balances are reported in Net worth, nothing more.
Overriding the rule
You can't change the rule per-category. If you want a category to not accumulate (a Fun money envelope where leftover should refund to Ready to Assign at month-end), do it manually: at month-end, move the surplus from Fun money back to a savings category or directly into next month by editing next month's Assigned.
A natural place to spot accumulation drift is the Assignment history report, which shows months of carry-in alongside Assigned and Activity for every category.