Function nper 

pub fn nper<C, P, F>(
    periodic_rate: f64,
    payment: C,
    present_value: P,
    future_value: F,
) -> FinanceResult<f64>
where
    C: Into<f64> + Copy,
    P: Into<f64> + Copy,
    F: Into<f64> + Copy,

Returns the number of periods for an annuity (payments) to reach a future value.

Related functions:

• nper_solution – same calculation with a solution struct
• nper_due – payments due at the beginning of each period

Formula (end-of-period payments):

n = ln( (pmt - fv * r) / (pmt + pv * r) ) / ln(1 + r)

Arguments

• periodic_rate – growth rate per period (e.g. 0.05 for 5%)
• payment – payment per period; must be negative (Excel convention) when PV/FV are ≥ 0
• present_value – present value (≥ 0 in the Excel-style sign convention used here)
• future_value – future value (≥ 0); at least one of PV/FV must be nonzero

Errors

Returns FinanceError when rate/payment/PV/FV cannot produce a finite period count.

Examples

use finance_solution::{nper, FinanceError};

let n = nper(0.034, -500.0, 1000.0, 20_000.0).unwrap();
assert!((n - 27.7879559).abs() < 1e-4);

assert!(matches!(
    nper(0.05, 100.0, 0.0, 1000.0),
    Err(FinanceError::InvalidCashflow { .. })
));