Free Late Payment Calculator
Calculate exactly how much interest is owed on an overdue invoice. Enter the amount, due date, and rate — see the total owed right now.
Free online tool
Late invoice interest calculated daily at your chosen annual rate. Includes total owing with interest accrued.
Late invoices hurt cash flow and can be legally recoverable if your payment terms are clear. This calculator shows you exactly how much interest has accrued and the total your client now owes.
Invoice details
ATO penalty interest rate is currently ~10% p.a.
Don't want to type all this?
SMASH does this automatically from a 30-second voice description. No form, no typing, no GST maths.
Try SMASH FreeInterest on commercial invoices is not automatic in Australia — you must state payment terms and interest conditions in your invoice or agreement.
How to use
Enter your invoice amount and due date
Enter the total invoice amount including GST, and the original due date. The calculator works from today's date to show you live days overdue.
Set your interest rate (default: 10% p.a.)
The default rate of 10% p.a. is aligned with the ATO's general interest charge rate. Adjust to match your payment terms — but make sure your terms state the rate clearly.
See how many days overdue and total interest owed
Your result shows the number of days overdue, interest accrued, and the total now owed including the original invoice. Use these figures in your overdue notice.
30+
Avg days overdue for tradie invoices
~10%
ATO reference interest rate p.a.
4.9★
App Store rating
How to get paid
Every day you delay sending the invoice is a day you push the payment back. Send it from the job site — before you even drive home.
Clients who can tap and pay in 10 seconds pay faster than clients who have to log in to internet banking and type your BSB. SMASH includes a Stripe Pay Now link on every invoice.
"I didn't get the invoice" is no longer an excuse. SMASH tells you exactly when your client opened the invoice. If they haven't — follow up.
Compare late payment tools
From tradies using SMASH
"The read receipts alone changed everything. I know exactly when my client opened the invoice — and I follow up immediately if they haven't paid."
Tony G.
Electrician, Sydney
"Had a client who 'forgot' for 45 days. Showed him this calculator and the invoice was paid within an hour."
Rachel B.
Cleaner, Canberra
"Late payments were killing my cash flow. SMASH shows me every overdue invoice and how many days they've been owing. I'm on top of it now."
Shane O.
Concreter, Brisbane
From the blog
FAQ
SMASH shows you every unpaid invoice, how many days overdue, and whether your client has even opened it. No more guessing.