This free invoice payment allocation planner helps you work out a fair way to spread one client payment across several open invoices, oldest first, and see what stays unpaid on each. It runs fully in your browser, needs no account, and gives a clear answer in seconds, so you can stop guessing and start with numbers you can trust. It is made for small business owners and freelancers, not for accountants, and every field is explained in plain words on the tool itself.
To use it, fill in the fields above and press the button. The tool checks your numbers, runs the calculation, and shows the result right below the tool. If a number looks wrong, change it and press the button again. Nothing is saved on a server, and you can use the tool as many times as you like, for one client or for many.
It follows the oldest-first rule used by most small businesses: the payment fills the oldest invoice completely before a single unit goes to the next one, then fills the second, then the third. Anything left over after all three invoices is shown as unallocated, and the remaining balance of each invoice is its original amount minus what was allocated to it.
For example, a payment of 700 against invoices of 500, 300 and 200 pays the oldest in full, puts 200 on the second, and leaves 100 on the second and 200 on the third unpaid. A payment of 1200 clears all three invoices and leaves 200 unallocated, which usually means an advance payment or an overpayment to clarify with the client.
Reading the result is simple: take the headline figure as your starting point, then check it against what you know about the real job. Prices, distances and payment habits all change from one client to the next, so a tool result is a strong guide, not a promise, and your own judgement still matters for the final decision.
Always tell the client how you allocated their payment, in the receipt or in a short message, because a client who expected the newest invoice to be paid will otherwise think the old one is still open. If a client asks for a different order, agree it in writing before you apply the payment.
A common mistake is trusting a single calculation and never checking it again. Re-run the tool when prices change, when a client changes the scope, or when a payment arrives late, because stale numbers quietly lead to undercharging and awkward conversations. Keep a short note of each result with the client name and the date, so you can explain any figure later without searching through old messages.
Over the next few weeks, use this tool as part of a simple weekly routine. Set aside a short time each week to update your figures, chase anything overdue, and review what the numbers are telling you about your business. A pattern over several weeks is far more useful than one good or bad day, because it shows which clients pay on time, which jobs earn well, and where your time actually goes. Small steady habits, repeated every week, build a business that is easier to run and easier to grow, and this tool is meant to make one small part of that routine faster and clearer.
This tool gives estimates for everyday business planning only and does not replace professional financial or tax advice. Use it to plan, to compare and to keep clear records, and ask a qualified professional when a decision involves large sums, contracts or tax rules. Try it with your own numbers now, and come back whenever a new invoice, quote or payment needs a quick, honest answer.