Financing guide

Convert nominal and effective annual rates to monthly rates

Distinguish nominal from effective rates and correctly convert annual percentages to a monthly period.

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Updated July 27, 2026

In this guide
  1. Equivalent effective rate
  2. Nominal rate
  3. Payment impact

Equivalent effective rate

An effective annual rate iₐ already includes compounding for the year:

iₘ = (1 + iₐ)1/12 − 1

Twelve percent effective annually is about 0.9489% monthly, not 1%.

Nominal rate

If 12% a year is nominal with monthly compounding, divide by 12: iₘ = 1%. That monthly rate yields about 12.6825% effective annually.

Payment impact

The module applies both readings to the same principal and term.

Hypothetical 12% annual rates used only to demonstrate nominal and effective conversion.

Parameters used

Financed amount
R$300,000.00
Term
360 months
Interest rate
12.00% effective per year
System
SAC
Monthly adjustment
—
Extra amortization
—

Calculated results

Scenario12% effective yearly12% nominal yearly
First paymentR$3,679.97R$3,833.33
Last paymentR$842.45R$842.88
Total interestR$513,820.18R$541,502.15
Total paidR$813,820.18R$841,502.15
Effective term360 months360 months
Accumulated adjustmentR$0.00R$0.00

Selected installments

Payment no.PaymentInterestAmortizationClosing balance
1R$3,679.97R$2,846.64R$833.33R$299,166.67
12R$3,592.99R$2,759.66R$833.33R$290,000.04
60R$3,213.44R$2,380.11R$833.33R$250,000.20
180R$2,264.56R$1,431.23R$833.33R$150,000.60
360R$842.45R$7.92R$834.53R$0.00
Outstanding balance over time12% effective yearly / 12% nominal yearly
Outstanding balance over time12% effective yearly12% nominal yearly
Open in simulator

Select the period and annual type exactly as the proposal states. “12% p.a.” alone does not provide enough information to choose safely.

What may differ in a contract

  • The proposal should identify period and rate type; do not assume every annual percentage is effective.
  • Annual CET contains other cash flows and cannot be converted as if it were only an interest rate.

Limits of this analysis

  • The formulas assume regular monthly compounding.
  • They exclude daily rates, business-day rules, grace periods and irregular flows.

Sources and review