Zoho Sheet ISPMT: Interest with equal principal reductions

=ISPMT(rate; period; nper; pv)

All four arguments are shown as required. Rate is the interest rate per payment period; period selects the point in the schedule; nper is the total number of periods; pv is the initial principal. There is no future-value or beginning/end-payment argument in this signature. Zoho ISPMT reference.

Use consistent time units. For a nominal annual rate of 12% charged monthly, the simple periodic conversion is 0.12/12 = 0.01. That conversion is an assumption about a nominal rate: an effective annual rate would need a different conversion. Enter percentages as decimal rates or percentage-formatted numeric inputs.

Enter these inputs in a fresh worksheet:

In B7 enter =ISPMT(B2;B3;B4;B5). The reference result is −120. Format B7 as a number or currency, not a percentage.

The model independently supported by Zoho’s complete published examples is:

interest = -pv * rate * (1 - period/nper)

Here the principal reduction per step is 10000/5 = 2000. At index 3, the remaining model balance is 10000 - 3*2000 = 4000. Multiplying by 0.03 and applying the cash-flow sign gives −120. Positive initial principal produces a negative interest payment while the remaining balance is positive.

This is a model with equal principal reductions. A constant-total-payment annuity has a different balance progression; do not use this linear formula as a substitute merely because the interest rate is fixed.

The public worksheet shows these complete rows and results:

Each matches the formula above. These are read-only vendor demonstration observations, not results from an authored Zoho workbook. Official published ISPMT example.

The first row is intentionally not a sensible loan schedule: period exceeds nper, and the remaining balance becomes negative, reversing the interest sign. Its presence shows why a numeric result alone does not establish a valid repayment model. Rate 15 means 1500%, not 15%.

For principal 1,000, periodic rate 1% and four equal principal reductions of 250, put indices 0, 1, 2 and 3 in A2:A5. In B2 enter =ISPMT(0.01;A2;4;1000) and copy down. The independent schedule is:

Index 0 represents the full initial balance in this model. At index 4, the model balance and interest are zero. Keep an index column separate from human-facing labels such as “Payment 1”: blindly using 1 for the first balance would omit the full-principal interest step.

The four interest amounts total −25. A separate independent arithmetic-series check is -1000*0.01*(4+1)/2 = -25. This sum assumes exactly the displayed zero-through-three schedule; it is not a universal total-interest formula for annuity loans or arbitrary period ranges.

Reversing pv to −1,000 reverses the model’s sign: index 2 gives +5. With a zero rate, the same valid schedule has zero interest. These independent checks help spot a sign or percentage-entry mistake before using a longer worksheet.

Use a positive whole-number nper and a deliberate schedule index. The short official error table does not establish detailed handling of nper zero, fractional indices, text coercion or every out-of-range input, so no exact runtime error is asserted for those cases here. Validate your inputs rather than treating an unverified error code as a contract.

PMT addresses a constant-payment calculation. PV and RATE answer different annuity questions. Check the intended amortization structure before choosing a function. This guide explains spreadsheet mechanics, not loan suitability, contractual charges or financial advice.

Zoho’s rolling help and published example were checked October 18, 2026. The worked schedules are independently calculated from the model supported by the three vendor rows. No account, uploaded workbook or authored native execution was used. First introduction version, historical lifecycle and mobile behavior are not established by these sources; a shared function name alone does not establish every boundary behavior across applications.