Free calculators
Deposit and savings interest calculator documentation
Inputs, formulas, assumptions and API/MCP examples for the deposit and savings interest calculator. Reproduce a calculation and cite its sources.
Content updated . Assumptions reviewed .
Formula and assumptions
Gross interest = P ((1 + APR/f)^(f months/12) - 1).
- Fractional compounding periods use the same exponential convention; rates are fixed for each deposit.
- Ladder principal is split equally; rung maturities and rate steps are entered assumptions. Matured proceeds earn no further interest.
- Early penalties equal entered months of simple nominal interest and may reduce principal, capped at the account balance.
- Tax applies only to positive interest after the penalty, at the entered rate; no jurisdictional deductibility rules are assumed.
Assumptions reviewed:
Sources
- KlarFort calculator methodology. KlarFort-authored arithmetic; free to use with credit.; vintage 1.
Parameters
| Name | Description | Type | Default | Minimum | Maximum |
|---|---|---|---|---|---|
| currency | Currency | string | "USD" | ||
| principal | Deposit principal | number | 10000 | 0 | 1,000,000,000 |
| annualRate | Nominal annual interest rate (%) | number | 4 | 0 | 100 |
| compoundsPerYear | 1 annual, 2 semiannual, 4 quarterly, 12 monthly, 365 daily. | integer | 12 | ||
| months | First deposit maturity months | integer | 12 | 1 | 600 |
| taxPercent | Tax rate on net positive interest (%) | number | 0 | 0 | 100 |
| withdrawAfterMonths | Withdrawal month (0 means each maturity) | integer | 0 | 0 | 600 |
| penaltyInterestMonths | Early penalty in months of simple interest | integer | 0 | 0 | 120 |
| mode | Deposit structure | string | "single" | ||
| ladderRungs | Ladder rungs | integer | 3 | 1 | 12 |
| ladderSpacingMonths | Months between ladder maturities | integer | 12 | 1 | 60 |
| ladderRateStep | Annual rate increase per rung (percentage points) | number | 0 | -20 | 20 |
JSON API
GET accepts one input parameter containing URL-encoded JSON. POST sends the JSON input object. Prefer POST for personal figures. Inputs are limited to 16 KiB. POST results are not stored; GET results may be cached for up to 24 hours.
curl -X POST https://klarfort.com/tools/api/v1/deposit-calculator -H "Content-Type: application/json" --data '{"currency":"USD","principal":10000,"annualRate":4,"compoundsPerYear":12,"months":12,"taxPercent":0,"withdrawAfterMonths":0,"penaltyInterestMonths":0,"mode":"single","ladderRungs":3,"ladderSpacingMonths":12,"ladderRateStep":0}'fetch("https://klarfort.com/tools/api/v1/deposit-calculator", {method:"POST", headers:{"Content-Type":"application/json"}, body:JSON.stringify({"currency":"USD","principal":10000,"annualRate":4,"compoundsPerYear":12,"months":12,"taxPercent":0,"withdrawAfterMonths":0,"penaltyInterestMonths":0,"mode":"single","ladderRungs":3,"ladderSpacingMonths":12,"ladderRateStep":0})})import json, urllib.request
request = urllib.request.Request("https://klarfort.com/tools/api/v1/deposit-calculator", data=json.dumps({"currency":"USD","principal":10000,"annualRate":4,"compoundsPerYear":12,"months":12,"taxPercent":0,"withdrawAfterMonths":0,"penaltyInterestMonths":0,"mode":"single","ladderRungs":3,"ladderSpacingMonths":12,"ladderRateStep":0}).encode(), headers={"Content-Type":"application/json"})
print(urllib.request.urlopen(request).read().decode())Connected assistants
Connect using https://klarfort.com/tools/mcp. Discover this calculator with tools/list, then call deposit-calculator. Protocol versions 2026-07-28 and 2025-11-25 are supported. Modern requests carry protocol metadata and matching HTTP headers. Set Mcp-Name to params.name for tools/call and to params.uri for resources/read. Older clients initialize first.
Limits: 120 requests per minute per address and approximately 3,000 per minute per edge location. Simulations are capped at 1,000 paths, 600 months and 150,000 path-months (paths multiplied by months). Shorten the duration or reduce paths when that work limit is exceeded. A limit response returns 429 and Retry-After. No exact remaining-request count is available.
Usage and credit
Free for personal, commercial and any other lawful use with credit to KlarFort at https://klarfort.com/. Third-party data terms still apply.
Place a visible credit near the reused material or in the credits for your work or integration. One clear credit per work or integration is sufficient; no separate credit per API request is required. Links to individual calculators are optional.
Computed with KlarFort Calculators, https://klarfort.com/
The API returns this text in credit and the homepage in credit_url. The optional citation_url identifies the calculator for reference. See usage and credit for the full permission.
KlarFort is not financial, investment, tax, or legal advice. Verify outputs before making material decisions.