Fidamen

Personal Loan Payment Calculator

This calculator helps you estimate bi‑weekly payments for a personal loan and compare common repayment approaches: standard monthly payments, standard bi‑weekly amortization, and the popular accelerated method (paying half the monthly payment every two weeks). Use the results to understand likely payoff time and interest savings.

Results are produced by standard amortization mathematics and a closed‑form solver for the number of periods when accelerated payments are used. The tool includes warnings where inputs make the math invalid (for example, when a periodic payment is too small to cover interest).

Updated Nov 11, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record f02f03068046 • Reviewed by Fidamen Standards Committee

Compute standard monthly payment, standard bi‑weekly payment, and the effect of paying half the monthly payment every two weeks (commonly called accelerated bi‑weekly). Estimates payoff time and interest saved.

Inputs

Results

Updates as you type

Monthly payment

-$1.94

Bi‑weekly payment (standard)

-$0.41

Accelerated bi‑weekly payment (half‑monthly)

-$0.97

Payoff time (years) — accelerated

—

Total interest — accelerated

—

Interest saved vs monthly

—

OutputValueUnit
Monthly payment-$1.94USD
Bi‑weekly payment (standard)-$0.41USD
Accelerated bi‑weekly payment (half‑monthly)-$0.97USD
Payoff time (years) — accelerated——
Total interest — accelerated—USD
Interest saved vs monthly—USD
Primary result-$1.94

Visualization

Methodology

We model loans with fixed nominal APR and periodic compounding corresponding to the payment frequency (monthly or bi‑weekly). Periodic rate = APR / payments_per_year.

Regular payment is computed from the standard annuity formula. For accelerated bi‑weekly (half‑monthly) we treat the submitted periodic payment and solve for number of periods using the logarithmic inverse of the annuity formula.

The calculator assumes fixed APR and fixed scheduled payments. It does not simulate extra unscheduled payments, fees, deferred interest, or negative amortization.

Worked examples

Example 1: $20,000 loan, 7% APR, 5 years. Monthly payment is computed, standard bi‑weekly payment (26/yr) is computed, and accelerated bi‑weekly (half monthly) reduces payoff time and interest by roughly the equivalent of one extra monthly payment per year.

Example 2: $10,000 loan, 10% APR, 3 years. Accelerated bi‑weekly payments can shorten the term by months and save several hundred dollars in interest compared with monthly payments, depending on APR and term.

F.A.Q.

Does paying bi‑weekly always save interest?

Paying bi‑weekly in itself does not automatically save interest unless the payment pattern results in more total payments per year than monthly payments or causes earlier principal reduction (for example, paying half the monthly payment every two weeks results in 13 monthly equivalents per year). The calculator shows the precise effect.

What is the difference between standard bi‑weekly and accelerated bi‑weekly?

Standard bi‑weekly amortization recalculates the scheduled payment for 26 periods per year. Accelerated bi‑weekly commonly means paying half the monthly payment every two weeks; this leads to 26 half‑payments (equivalent to 13 monthly payments) and typically shortens the loan term.

Are these results exact?

Results follow closed‑form amortization formulas and a log solution for periods. They are exact within the mathematical model used (fixed APR, fixed payment schedule). Real lender statements may vary due to rounding, daily interest accrual conventions, fees, and payment processing timing.

What if the calculator shows a domain error (invalid log)?

A domain error in the logarithmic solver indicates the periodic payment provided is too small to cover the periodic interest (payment less than or equal to the interest due for the period). Increase the payment, APR, or shorten the term to resolve.

Sources & citations

Further resources

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: f02f03068046

What changed (latest)

v1.0.0 • 2025-11-11 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 11, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-11 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: c60e611a2381