Monthly Budget Split
Divide monthly income into needs, wants and savings.
Enter your numbers
Formula
How the calculation works
The split is three multiplications of the same base, one per share, so the parts rebuild the whole only when the shares add to 100. That is why the tool stops instead of guessing when they do not: with shares of 50, 30 and 25 the three parts would sum to 105% of the income, and the extra would have to be funded by borrowing.
The percentages are a convention, the 50/30/20 rule popularised as a simple budgeting guide, not arithmetic truth. What is arithmetic is that the ratio is scale-invariant: 3,000 and 9,000 split into exactly the same proportions, and only the money changes. The rule says nothing useful until you fix the income it applies to.
The hard part is not the multiplication but the sorting. Rent, food and transport are needs; a streaming subscription is usually a want; a pension contribution is savings. The same line can move category with circumstance, since a car needed to reach work is a need and one kept for weekends is not. The tool computes; the judgement is yours.
Common mistakes
- Making the shares add to more than 100, or working them out by eye. The tool stops, because if the three percentages do not total 100 the parts do not rebuild the income and one of them is being paid for by debt.
- Treating the split as a rigid ceiling. If needs genuinely run past 50%, the thing to adjust is the savings target or the housing cost, not to relabel the rent as a want and pretend the plan balances.
- Running the 50/30/20 on gross pay when the bills are paid from net. The split belongs on take-home pay, because 20% of gross is more money than 20% of what actually lands in the account.
When to use it
- Use it to turn a monthly income into three concrete numbers, and to see what shifting one share does to the other two before you commit to a budget for the month.
- It is the wrong tool for tracking what you actually spent, since it sets a plan and keeps no record. With an irregular income, split a realistic average month and hold a buffer, because a fixed percentage of a month with no work is still zero.
Worked example
On 3,000, a 50/30/20 split is 1,500 needs, 900 wants, 600 savings.
Common questions
What if the shares do not add to 100?
The result would not be meaningful, so the calculator stops rather than showing a quietly wrong figure.
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