Fidamen

Boat Loan Extra Payments Calculator with Bi-Weekly Payments

This calculator models a boat loan amortization schedule when you make regular payments and optionally add extra recurring payments or a lump-sum prepayment. It supports both monthly (12/year) and bi-weekly (26/year) frequencies and reports estimated payoff time and total interest paid.

Results are estimates for planning purposes. The calculator applies standard amortization math and assumes the lump-sum prepayment, if used, is applied at loan start. For payments applied at other times during the loan term, estimated effects may differ; consult your loan servicer for an exact payoff quote.

Updated Nov 24, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 6a47c0fe7584 • Reviewed by Fidamen Standards Committee

Estimate payoff and interest when making 26 payments per year (bi-weekly) plus optional recurring extra payments and an optional lump-sum prepayment applied at loan start.

Inputs

Results

Updates as you type

Base bi-weekly payment (no extras)

$179.17

Actual bi-weekly payment (including extra)

$179.17

Estimated payoff (periods)

260

Estimated payoff (years)

10

Estimated total interest paid

$11,582.93

Estimated interest saved vs scheduled payments

$0.00

OutputValueUnit
Base bi-weekly payment (no extras)$179.17USD
Actual bi-weekly payment (including extra)$179.17USD
Estimated payoff (periods)260—
Estimated payoff (years)10—
Estimated total interest paid$11,582.93USD
Estimated interest saved vs scheduled payments$0.00USD
Primary result$179.17

Visualization

Methodology

Periodic interest rate = APR / payments per year. Payment amounts use the standard annuity formula for level payments: A = P * r / (1 - (1 + r)^-N).

When recurring extras or a lump sum are applied, the tool recomputes the remaining payoff periods by solving the amortization equation for N using logarithms. Total interest is then approximated as total payments (periodic payments × periods + lump sum) minus original principal.

Calculations use conservative numerical techniques appropriate for browser-based financial tools. Edge cases (zero interest rate, zero extra payments, or payments that do not cover interest) are handled with safeguards; the tool will warn if the inputs would not amortize the loan.

Worked examples

Example: $35,000 loan, 6% APR, 10 years. Making bi-weekly payments (26/year) with an extra $25 per bi-weekly payment reduces payoff years and saves interest compared to the scheduled monthly-only payments.

Example: A one-time lump-sum prepayment at loan start immediately reduces principal and shortens payoff; the tool assumes lump-sum is applied at start for the estimate.

F.A.Q.

Does bi-weekly always save money versus monthly?

Bi-weekly frequency can reduce interest primarily because 26 payments a year often equals one extra monthly payment annually compared to 12 monthly payments. Savings depend on payment amounts and whether you add recurring extras. Use the compare mode to see estimated differences for your exact inputs.

Can I model a lump-sum prepayment made later in the term?

This version applies lump-sum prepayments at loan start for estimates. Prepayments made later change the outstanding principal and interest; for exact results, request a payoff schedule from your lender or use a detailed amortization tool that simulates payments period-by-period.

How accurate are the numbers?

Results use standard annuity math and solve the amortization equation analytically. Calculations follow common numerical practices and account for rounding to reasonable precision. See citations for standards on numeric accuracy. For legally binding figures, get a written payoff from your loan servicer.

What if the periodic payment does not cover interest?

If the entered payment (base + extra) is less than or equal to the periodic interest, the loan would not amortize. The tool detects this and will indicate the inputs do not produce payoff. Increase the payment or reduce term to produce a valid amortization.

Sources & citations

Further resources

External guidance

Versioning & Change Control

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

Record ID: 6a47c0fe7584

What changed (latest)

v1.0.0 • 2025-11-24 • 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 24, 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 • 2025-11-24 • 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: d5e57394b24a