Start with expenses you would still need to pay
Make a monthly list of housing, basic food, essential transport, utilities, required insurance and minimum debt payments. Separate optional spending from obligations that would continue if income stopped. Use your own amounts instead of an average household budget.
If essential expenses are 2,000 a month, a chosen four-month buffer is 8,000. With 3,000 already reserved for emergencies, the remaining gap is 5,000. Saving that gap over 20 months, with no assumed interest, requires 250 per month.
These are arithmetic scenarios. The chosen number of months is not a universal recommendation. Income reliability, dependants, insurance, upcoming obligations and access to support can change what feels workable for you.
Keep the same savings from being counted twice
Money already committed to next month's rent or a planned purchase may not be available for an emergency. If one savings account serves several purposes, allocate it explicitly before entering an existing emergency balance.
The emergency fund tool calculates the target and the gap. The savings goal tool turns that gap into a monthly amount over your chosen deadline. Neither assumes an investment return.
Revisit the inputs after a real change
A change in rent, household size, transport or income can make an old target less useful. Updating those assumptions is more meaningful than changing a page date each month. Keep a copy of the inputs alongside the result so that a future comparison explains why the target moved.