Fidamen

Boat Loan APR Calculator with Extra Payments

This calculator models a boat loan using standard amortization math and lets you add a fixed extra payment each payment period to show the impact on total interest and time to payoff. It also provides an approximate APR that spreads upfront fees across the loan term for planning purposes.

Use the inputs to represent your quoted rate, term, and any fees. Enter any recurring extra payment you plan to make each payment period (for example, an extra monthly amount). Results are estimates for planning and not a substitute for the lender's official disclosure.

Updated Nov 19, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 85fa05e14987 • Reviewed by Fidamen Standards Committee

Calculates the regular payment for the loan term and projects the impact of a constant extra payment applied each payment period. Provides total interest paid, total paid, and estimated payoff time in years.

Inputs

Results

Updates as you type

Scheduled payment (no extra)

-$1.58

Payment including extra

-$1.58

Estimated payoff time

-73.981

Estimated total interest

-$33,597.44

Estimated total paid

$1,402.56

OutputValueUnit
Scheduled payment (no extra)-$1.58—
Payment including extra-$1.58—
Estimated payoff time-73.981years
Estimated total interest-$33,597.44—
Estimated total paid$1,402.56—
Primary result-$1.58

Visualization

Methodology

Payment calculations use standard amortizing loan formulas: the per-period interest rate is annual_rate_pct divided by payments per year. The scheduled payment (without extra) uses the annuity formula.

When a recurring extra payment is specified, the calculator treats it as an additional constant payment each period and computes the theoretical payoff time by solving the amortization equation for the number of periods.

The APR estimate method shown here is an approximation that spreads the effect of upfront fees across the scheduled payments to produce an annualized percentage. Precise APR as defined by regulation may require solving an internal rate of return on cash flows; consult lender disclosures for the legally required APR.

F.A.Q.

Is the APR shown here the official APR on my loan documents?

No. The APR shown by this calculator is an approximation intended for planning and comparison only. Legal APR disclosures follow regulatory rules and may use a different method or include additional finance charges. Always review the lender's Truth-in-Lending disclosure for the official APR.

How does an extra payment reduce interest and payoff time?

An extra payment reduces the outstanding principal more quickly. Since interest accrues on the remaining principal, reducing principal faster lowers future interest, shortening the loan term and reducing total interest paid.

Are fees included in the loan amount for APR?

This tool allows you to enter upfront fees to see an approximate APR effect. Some fees may be financed, some paid separately; the exact APR calculation depends on which fees are included by the lender and regulatory definitions.

How accurate are the payoff time and interest estimates?

Estimates use standard closed-form amortization formulas. Accuracy depends on exact payment timing, day-count conventions, compounding rules, and whether fees are financed. For legal or contractual purposes rely on lender-provided amortization tables and disclosures.

Sources & citations

Further resources

Versioning & Change Control

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

Record ID: 85fa05e14987

What changed (latest)

v1.0.0 • 2025-11-19 • 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 19, 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 • 2025-11-19 • 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: 7ef3ecc31937