How long will my money last?

What a money runway actually tells you

Your runway is the number of days your current cash survives once every known bill and every expected paycheque is placed on the calendar. It is the single most useful number in personal finance, and almost no budgeting app shows it, because most of them are built to categorise money you already spent rather than to project money you have not spent yet.

The arithmetic is simple, which is exactly why it works: start with what is in the account today, walk forward one day at a time, subtract each bill on the day it actually leaves, add each paycheque on the day it actually lands, and record the closing balance. The first day that closing balance would fall below zero is the end of your runway. If it never falls below zero inside the window, you are covered, and the number that matters instead is your lowest point.

Why averages lie about how long your savings will last

Divide monthly bills by monthly income and you get a tidy, comforting ratio. Real life is lumpier. Rent leaves on the first, insurance on the fifth, the card payment on the eighth, and your pay might not arrive until the twelfth. A month that balances perfectly on average can still have a week where you are three hundred dollars short - which is when overdraft fees, missed payments and card interest actually happen.

Projecting day by day surfaces those dips before they arrive. It also surfaces the good news: if you are paid every two weeks, twice a year you receive three paycheques in one calendar month. A monthly average quietly eats that extra pay. A day-by-day forecast shows it as a visible bump you can aim at a debt, a repair or a buffer.

How to get a useful answer in two minutes

• Cash on hand: the real balance in your everyday account right now, not including savings you refuse to touch.
• Income: what actually lands in the account after deductions, and how often. Pick your next payday from the calendar so the cycle lines up.
• Bills: everything that recurs - housing, utilities, phone, insurance, groceries, subscriptions, minimum debt payments. Being slightly pessimistic here makes the answer more useful, not less.

What to do with the number

If your runway is short, the fastest lever is usually timing rather than heroic frugality: moving a bill’s due date a week later, or splitting one large annual charge into a monthly set-aside, can remove a dip entirely. If you are covered, aim at the lowest point instead - the buffer you keep above zero is what turns a surprise car repair from a crisis into an inconvenience.

In Lastwell this projection stays live: cards, loans and one-off plans all feed the same engine, and the assistant answers spend questions with the number this page calculates.