Walkthroughs guide
How to Chase an Overdue Invoice: Interest Calculator to New Invoice Walkthrough
From late-fee calculation to a fresh invoice for the full amount owed.
When a client hasn't paid on time, there are two separate jobs: working out how much interest and fees you can add, and then getting a proper invoice in front of them for the full new amount. This guide walks through both, using TidyPapers' Late Payment Interest Calculator (/late-fee-calculator/) and the invoice generator (/). One button moves the numbers between them: the calculator's "Create reminder invoice" button queues the original amount and the accrued interest/fees as ready-made line items, so you don't have to copy the figures by hand.
Before you start
You'll need:
- The original invoice amount and its due date
- The invoice reference/number
- Whether EU statutory interest applies to you, or you're setting your own rate
Part 1 — Calculate what's owed now
Step 1 — Enter the invoice basics
- Go to https://tidypapers.com/late-fee-calculator/.
- Enter the Invoice amount and set Currency (€ Euro (EUR), $ US Dollar (USD), or £ British Pound (GBP)).
- Enter the Invoice due date.
- Leave Calculation date as today (it defaults to today), or change it to a future date if you're planning ahead.
- Fill in Invoice reference (optional, used in the copied reminder text) — it also becomes part of the line-item description if you use the "Create reminder invoice" button in Step 5, so it's worth adding.
On the live toolthe invoice amount, currency, due date, calculation date, and invoice reference fields filled in
Step 2 — Choose your interest basis
Set Interest basis to one of:
- EU statutory (Late Payment Directive 2011/7/EU) — then fill in ECB reference rate (use the page's "Check the current ECB reference rate ↗" link to look it up); the Statutory margin is fixed at "+8 percentage points" and applied automatically.
- US / custom — then fill in your own Annual interest rate (%).
Optionally tick Fixed late fee amount (optional, in addition to interest) and enter an amount if your terms allow a flat fee on top of interest.
On the live toolthe Interest basis toggle with one option selected and its corresponding rate field(s) filled in
Step 3 — Calculate and read the results
- Click "🧮 Calculate late fees →".
- Note the five results: Days overdue, Daily interest, Accrued interest, Flat fees, and — the number you actually need for the new invoice — Total owed now.
On the live toolthe results panel with Total owed now highlighted
Step 4 — Copy the reminder text (optional, for a first nudge)
If you just want to send a polite reminder before issuing a full new invoice, click "📋 Copy demand text →" and paste the copied text into an email. This is useful as a first-touch nudge and doesn't affect the reminder invoice in Step 5 — you can do either, both, or one after the other.
On the live toolthe Copy demand text button with its ✓ confirmation
Part 2 — Send "Total owed now" to a new invoice
Step 5 — Create the reminder invoice
Click "Create reminder invoice." This queues two line items for the invoice generator: one for the original invoice amount (labeled with your invoice reference from Step 1, if you added one), and one for the accrued interest and fees combined. The calculator's currency comes with them. A confirmation line appears on the page: "Reminder invoice ready — open the Invoice Generator to download it."
On the live toolthe "Create reminder invoice" button clicked, with the "Reminder invoice ready" confirmation text visible
Step 6 — Open the invoice generator
- Go to https://tidypapers.com/.
- A banner reads "2 line items received from Late Payment Interest Calculator," and both line items — the original amount and the interest/fees — are already in the invoice, with the currency already matching the calculator.
- Your saved business details (name, VAT/tax ID, logo) should already be filled in if you've used any TidyPapers tool with the shared business profile before.
- Enter or confirm the client's name — the client name isn't part of the handoff, so add it here.
On the live toolthe invoice generator open with the "received from Late Payment Interest Calculator" banner and both line items already present
Step 7 — Check the totals, then generate and send
- Check the invoice total matches the calculator's Total owed now figure from Step 3 — the two line items should add up to it, but it's worth a glance since you can still edit either line item's description or amount before sending.
- Click "📄 Download PDF →".
- Send the PDF to the client, ideally alongside (or shortly after) the reminder text you copied in Step 4 so the client has context for why the total changed.
On the live toolthe final invoice PDF preview showing the total matching the calculator's Total owed now figure
What is and isn't automatic in this workflow
| Step | Automatic or manual? |
|---|---|
| Interest and total-owed calculation | Automatic (within the calculator page) |
| Reminder text pre-filled with your invoice reference | Automatic, once you've typed it into the Invoice reference field |
| Original amount and interest/fees appearing on the new invoice as line items ("Create reminder invoice") | Automatic — click the button, then open the invoice generator |
| Client name on the new invoice | Manual — not part of the handoff, add it on the invoice generator |
| New invoice remembering your business details | Automatic (shared business profile, once saved) |
Frequently asked practical questions
Should I send the reminder text or a new invoice first?
Either can work depending on your relationship with the client — a copied reminder (Step 4) is lighter-touch for a first nudge; a fully re-issued invoice with separate interest/fee line items (Steps 5–7) is more formal and gives the client a clear document to pay against. You can do both — they don't interfere with each other.
Do I need to recalculate if the client still doesn't pay?
Yes — interest accrues daily, so if time passes before payment, go back to the calculator, update the Calculation date, recheck Total owed now, and click "Create reminder invoice" again for an updated pair of line items.
Can I add multiple overdue invoices to one calculation?
No — the calculator works on one invoice amount and one due date at a time; for several overdue invoices, run the calculator separately for each one and click "Create reminder invoice" for each (or issue separate invoices).
What if I already had other line items on the invoice generator?
The two received line items are added alongside whatever's already there — the invoice generator only clears a single still-empty starter line item to make room for the first thing it receives; anything you'd already filled in stays.