BEHIND THE NUMBERS
How this calculation works
Worked example
JPY 10,000 compounded through three complete ten-day periods becomes 10,000 × 1.1³ = JPY 13,310. Simple interest over the same 30 days would give JPY 13,000.
Example result: JP¥13,310
Ten-day rates accumulate quickly
A rate that looks small per short period can produce a substantial cost. Simple annualisation of 10% per ten days is 365% over 365 days; compounding gives a different, much larger annual balance.
Partial periods must be visible
At 11 days, charging a started period gives two full charges; completed periods give one. Prorating adds one day of the stated ten-day rate after the first complete period.
Assumptions and rounding
- The ten-day rate is fixed at 10%, the defining Toichi convention.
- For prorated compounding, the final incomplete period adds 1% per remaining day to the balance after completed periods. Yen amounts are rounded once at the end.
Questions about this calculator
Is the displayed amount legally payable?
That cannot be determined from this arithmetic. Applicable lending law and the agreement need separate examination.
Is the annualised percentage an APR?
No. The displayed comparison is a simple 365-day annualisation and excludes fees and regulated APR conventions.