How to use the age of money calculator
- Paste your income and spending, one per line, with a date first and an amount last. Income is positive and spending is negative or in brackets.
- You may put a note between the date and the amount, and lines starting with # are skipped.
- Choose how many of the most recent spends to average.
- Read the age of money in days, the unspent income left and the age of each spend in the table.
Formula
sort by date, with income before spending on the same day
each spend uses the oldest income that is still unspent (first in, first out)
age of a spend = sum of dollars x days since earned / dollars spent
age of money = the same dollar weighted average over the last N spends
Every dollar is matched to a dollar of income. Amounts are handled in whole cents, so there is no rounding in the matching.
Two months of pay
Paychecks of $2,000 arrive on January 2, January 16 and February 3. Rent of $900 on January 3 uses money earned on January 2, so it is 1.0 day old. Groceries of $150 on January 10 use the same pay and are 8.0 days old, and utilities of $200 on January 20 are 18.0 days old, because they still draw on the first paycheck.
Over all six spends the dollar weighted age is 16.5 days. Looking only at the last three spends gives 26.7 days, and $3,270 of income is still unspent at the end. In a month where all pay is spent within days, as in the third preset, the age falls to 2.7 days.
What a rising age tells you
A small age means money is spent soon after it arrives, so a late paycheck would be felt quickly. A larger age means some of what you spend was earned weeks ago, which gives you a buffer. The number is a way to watch that buffer grow as you build savings, and it does not say how much to save.
Pair it with the Emergency Fund Calculator for a savings target, the Irregular Income Budget Planner if your pay arrives unevenly, and the Budget Planner for a monthly plan.
What to leave out
Transfers between your own accounts are not income or spending, so leave them out or the ages will be wrong. If spending is larger than the income received before it, the tool names the date and the shortfall so you can add the missing income, such as a balance from before your list begins.
Assumptions and limits
- Income and spending dates are the days money was received and spent.
- Spending always uses the oldest unspent income first.
- Your list starts with income that covers the first spend, or you add a line for the balance you started with.
- Only the text you paste is used, and it stays in your browser.
Frequently asked questions
Why average only the latest spends?
The age of money is meant to show where you are now. An average over a long history is hard to move, so the tool lets you choose how many of the latest spends count.
Which date format can I use?
Use 2026-01-05 or 1/5/2026, where the first number is the month. A line that does not start with a real date is reported with its line number.
Can the age of money be zero?
Yes. If you spend money on the same day you receive it, the matched dollars have no days between them, and the age of that spend is 0.0 days.
Does this work with several accounts?
Paste them together and leave out transfers, and the tool treats them as one pool of money. If you want each account on its own, run them one at a time.