TrueCalci

Compound wealth growth

compound_wealth

Read-onlyIdempotent

Standard precision: this calculator uses ordinary floating-point arithmetic, keeps no dated table of official rates, and has not yet passed our full reference-test suite. Simulate long-term compound interest growth for retirement portfolios, 401(k)s, Roth IRAs, UK ISAs, or European ETF savings plans (Sparplan) with recurring monthly deposits.

Behavior: Deterministic, idempotent calculation with zero external side effects. Applies discrete compound interest formula with periodic annuity deposits: Future Value = P*(1 + r/n)^(nt) + PMT(((1 + r/n)^(n*t) - 1)/(r/n)). Returns final accumulated balance, total principal contributed, total compound interest earned, and annual wealth progression milestone table.

Usage Guidelines: Use for multi-year personal wealth projection and retirement nest-egg simulations. Do not use for Indian mutual fund monthly SIPs with annual step-up; use sip_investment instead.

Input Schema

TableJSON Schema

Name	Required	Description
`principal`	No	Initial lump-sum deposit or starting balance in currency units. Must be non-negative.
`tenureYears`	Yes	Investment horizon in years (e.g. 10, 20, 30). Must be an integer >= 1.
`monthlyDeposit`	No	Recurring monthly contribution added to the account. Must be non-negative.
`annualRatePercent`	Yes	Expected annualized investment return rate percentage (e.g. 8 for 8%). Must be positive.
`compoundFrequency`	No	Number of compounding periods per year (1 for annual, 4 for quarterly, 12 for monthly).

Output Schema

TableJSON Schema

Name	Required	Description	Default
`principal`	No
`futureValue`	No
`totalInterest`	No
`totalDeposited`	No
`yearlySchedule`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 27, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "futureValue": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "principal": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalDeposited": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "totalInterest": {
+      "type": [
+        "string",
+        "number",
+        "null"
+      ]
+    },
+    "yearlySchedule": {
+      "type": [
+        "array",
+        "null"
+      ]
+    }
+  },
+  "type": "object"
+}

Changed2 schema fields changedSep 24, 2026
- removedInput schema / properties / annualRatePercent / default
```
Removed value: -8
```
- removedInput schema / properties / tenureYears / default
```
Removed value: -15
```

Changed5 schema fields changedSep 5, 2026

changedInput schema / properties / annualRatePercent / description

Previous value: -"Expected annual return in %"New value: +"Expected annualized investment return rate percentage (e.g. 8 for 8%). Must be positive."

changedInput schema / properties / compoundFrequency / description

Previous value: -"Compounding frequency per year (12 = monthly)"New value: +"Number of compounding periods per year (1 for annual, 4 for quarterly, 12 for monthly)."

changedInput schema / properties / monthlyDeposit / description

Previous value: -"Monthly recurring contribution"New value: +"Recurring monthly contribution added to the account. Must be non-negative."

changedInput schema / properties / principal / description

Previous value: -"Initial principal deposit"New value: +"Initial lump-sum deposit or starting balance in currency units. Must be non-negative."

changedInput schema / properties / tenureYears / description

Previous value: -"Duration in years"New value: +"Investment horizon in years (e.g. 10, 20, 30). Must be an integer >= 1."

First observedSep 5, 2026

TDQS

A4.6/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior, so the description's repetition of determinism and zero side effects adds little. However, it goes beyond annotations by disclosing precision limitations ('ordinary floating-point arithmetic,' 'no dated table of official rates,' 'not yet passed our full reference-test suite'), the exact formula used, and the return contents.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with clear sections for precision caveat, purpose, behavior, and usage. It is slightly less front-loaded because the precision caveat comes before the purpose, and the deterministic/idempotent/zero-side-effects sentence duplicates annotation data, but no sentence is seriously wasteful.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity, rich annotations, and an existing output schema, the description is complete enough: it covers purpose, usage boundaries, calculation method, precision caveats, and the alternative tool. An agent has everything needed to invoke it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The description adds useful semantic mapping via the formula: P corresponds to principal, r to annualRatePercent, n to compoundFrequency, t to tenureYears, and PMT to monthlyDeposit, clarifying how the parameters interact.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Simulate long-term compound interest growth for retirement portfolios... with recurring monthly deposits.' It explicitly distinguishes itself from the sibling tool sip_investment for Indian mutual fund SIPs, so an agent can route correctly without inspecting schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives clear when-to-use guidance: 'Use for multi-year personal wealth projection and retirement nest-egg simulations.' It also gives an explicit exclusion and alternative: 'Do not use for Indian mutual fund monthly SIPs with annual step-up; use sip_investment instead.'

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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