Fidamen

Personal Loan Interest Calculator

This calculator estimates periodic payments, total interest, and total cost for a personal loan when making bi‑weekly payments (or other payment frequencies). You can include an optional extra amount per payment to see how additional principal reduces interest and term.

Results are estimates based on standard amortizing loan math: interest is calculated per payment period from the APR and compounded at the same frequency as payments. Fees, taxes, late charges, and changes in APR are not included.

Updated Nov 8, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 662f5a853001 • Reviewed by Fidamen Standards Committee

Inputs

Results

Updates as you type

Scheduled periodic payment (without extra)

$143.35

Periodic payment (including extra per payment)

$143.35

Number of payments

78

Total amount paid over life of loan

—

Total interest paid

—

Reference monthly payment (for comparison)

$311.06

Total interest if paid monthly (reference)

$1,198.24

Estimated interest savings vs monthly schedule

—

Percent reduction in interest vs monthly schedule

—

OutputValueUnit
Scheduled periodic payment (without extra)$143.35USD
Periodic payment (including extra per payment)$143.35USD
Number of payments78—
Total amount paid over life of loan—USD
Total interest paid—USD
Reference monthly payment (for comparison)$311.06USD
Total interest if paid monthly (reference)$1,198.24USD
Estimated interest savings vs monthly schedule—USD
Percent reduction in interest vs monthly schedule——
Primary result$143.35

Visualization

Methodology

Periodic rate = APR / 100 / (payments per year). Number of payments = term (years) × payments per year.

Scheduled payment formula uses the standard fixed‑payment annuity formula. Optional extra per payment is added on top of the scheduled payment and reduces principal sooner, lowering total interest and potentially shortening effective term.

Key takeaways

Use the frequency selector to choose bi‑weekly (default) or another cadence. Enter principal, APR, term, and any extra per payment to estimate payment size, total interest, and how much you might save versus a monthly schedule.

This tool follows standard annuity formulas and cites standards for numerical accuracy; treat the results as planning estimates and verify exact payoff figures with your lender.

F.A.Q.

Does bi‑weekly always save interest versus monthly?

Bi‑weekly schedules can reduce interest when the lender treats bi‑weekly as 26 equal payments per year because the timing and number of payments can reduce average outstanding principal. Actual savings depend on how your lender applies payments and whether they accept partial payments or apply extra payments to principal immediately.

Are fees, prepayment penalties, or changing APRs included?

No. This calculator excludes fees, penalties, variable APRs, and taxes. If your contract includes prepayment penalties or origination fees, include those separately in total cost calculations.

What happens if APR is zero?

For a 0% APR loan, the scheduled payment equals principal divided by number of payments. Some formula terms may be undefined at zero interest; the calculator will treat the 0% case as a simple division of principal by number of payments.

How accurate are the results?

Results are numerical estimates. Rounding, lender rounding rules, payment application timing, and special contractual terms can create small differences. Use outputs for planning; consult your loan servicer for exact payoff schedules.

Can I use this for mortgages or credit cards?

The math applies to any amortizing loan with a fixed APR and fixed periodic payments. Mortgages often include escrow, insurance, and taxes; credit cards typically use daily compounding and variable balances — those require different calculators.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: 662f5a853001

What changed (latest)

v1.0.0 • 2025-11-08 • 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 8, 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 • 2025-11-08 • 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: c0af1b40200a