Calculate overdue rent interest using simple or daily compound accrual, grace days, a flat fee, and reverse targets for days or annual rate.

Arithmetic estimate in USD. Rates, fees, compounding and grace periods must be permitted by your lease and local law; this tool does not determine legality.

Optional settings

Blank means 0. Interest starts after these days.

Blank means 0. Added once, even within the grace period; excluded from interest targets.

Late Rent Interest Formula

Select simple daily interest or daily compounding with a 365- or 360-day basis. All amounts use USD; the arithmetic does not determine whether a charge is legally allowed.

I = R × (r / 100) / 365 × d
  • I = interest due
  • R = rent amount
  • r = annual interest rate as a percent
  • d = max(0, calendar days overdue − non-interest grace days)

For simple interest on the 365-day basis, the calculator rearranges the formula for days or annual rate. The principal formula below is included for reference:

d = I / (R × (r / 100) / 365)
r = (I / (R × d)) × 365 × 100
R = I / ((r / 100) / 365 × d)

The formulas above assume simple interest and a 365-day year. For daily compounding, I = R × [(1 + r/100/B)^d − 1], where B is 365 or 360. The calculator subtracts the entered non-interest grace days and adds a permitted one-time fee separately. Simple forward interest rounds once to cents; compound estimates do not round each day. It excludes payments, varying rates and court costs. A zero target is reached on day 0; a rate cannot be uniquely inferred during grace. Check the lease and applicable landlord-tenant law before charging interest.

Useful Late Rent Interest Tables

Use this table to estimate how quickly interest adds up for each $1,000 of unpaid rent.

Annual interest rate Interest per day per $1,000 Interest for 30 days per $1,000
3% $0.08 $2.47
5% $0.14 $4.11
10% $0.27 $8.22
12% $0.33 $9.86
18% $0.49 $14.79

These inputs control the result.

Input What to enter
Rent amount The unpaid rent balance, not including separate late fees.
Annual interest rate The yearly rate allowed by the lease or law.
Days late Calendar days since the due date; the calculator separately subtracts the entered non-interest grace days.
Interest due The dollar amount of interest owed for the late period.

Late Rent Interest Example

If rent is $1,500, the annual interest rate is 10%, and payment is 14 days late, the interest is:

$1,500 × 0.10 ÷ 365 × 14 = $5.75

The example gives interest only, with no grace days. In Interest and total due mode, the primary result adds unpaid rent, rounded interest and the entered one-time fee. Only include charges permitted by the lease and applicable law.