Rent Overpayment Interest Calculator

Increasing Principal Sum method · simple interest, s.69 County Courts Act 1984

Worked the way a county court reads it: each overpayment joins the running balance on the day it was paid, and simple interest at 8% a year (County Courts Act 1984, s.69) is charged on that balance for the days until the next payment. A late first payment does not shift the rest — later payments are counted on the day the rent falls due. Nothing you type is stored or sent anywhere. Close the page and it is gone.

Rent Overpayment Interest Calculator

I built this tool to work out exactly how much my property agent owed me after an error led to an ongoing rent increase. Once I had the sums right for myself, I put it online for free to save other tenants the headache of working it out by hand.

The legal bit

This tool is a guide, not formal legal advice. The arithmetic follows the way county courts read a claim for interest, but you use it at your own risk. Double-check your final figures with Citizens Advice or Shelter before putting them to a court, a tribunal, or in a Letter Before Action. I am not a solicitor and accept no liability for your claim.

How the sums work — the increasing principal sum

Most calculators put interest on one lump sum from one date. That is wrong for rent overpayments, because you paid month by month: the principal sum owed to you was increasing the whole time. Your first overpayment has been held the longest and earns the most interest; your last one the least. This tool adds each payment to the running balance on the day it was made, charges simple interest on that balance for the days until the next payment, and adds it all up. A late first payment does not shift the rest — later payments are counted on the day the rent falls due.

Your data

Everything runs in your browser. Nothing you type is stored, sent anywhere, or remembered — close the page and it is gone. The 8% rate is the usual county-court rate (County Courts Act 1984, s.69); you can change it if the court directs a different one.

Where to find it — the official pages for EPCs, deposits, owners and the law →

Date of the first overpayment (the day it was actually paid)

How often the rent is paid

Day of the month the rent falls due

Overpaid each time (£) — what you paid minus what was due

Still going on?

Work it out as at

Interest rate (% a year)

Payments

Sums overpaid

£0.00

Interest to date

£0.00

Total

£0.00

How the interest is worked out. Simple interest at 8% a year under section 69 of the County Courts Act 1984, claimed from the date each sum was paid. It is worked on an increasing principal sum: when each payment is made it joins the running balance, and interest for the days until the next payment is charged on that running balance only (balance × rate × days ÷ 365). Interest is never charged on interest. The same total results from charging every payment its own interest from its own date and adding them up. Whether to award interest, and at what rate, is for the court.

Statement — one line per payment

#	From	To	Days	Paid	Balance	Interest this period	Running total

Prepared with the Savvy Renter rent overpayment interest calculator (savvyrenter.co.uk, increasing principal sum) on . Figures only. Nothing entered here is stored or sent anywhere.