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jenbreese merged 9 commits into from
May 22, 2026
Merged

IDFM-183: Compounding frequency Calculator - client feedback #109

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IDFM-183: Caps and design edits
jenbreese May 18, 2026
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New feedback from Excel sheet
jenbreese May 19, 2026
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jenbreese May 19, 2026
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jenbreese May 20, 2026
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jenbreese May 20, 2026
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jenbreese May 20, 2026
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jenbreese May 22, 2026
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jenbreese May 22, 2026
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jenbreese May 22, 2026
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275 changes: 217 additions & 58 deletions app/interactives/compounding-frequency-calculator/page.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,17 +42,20 @@ function calculateCompoundInterest(
return { finalAmount, interestEarned, totalPeriods }
}

const MAX_INITIAL_AMOUNT = 50_000_000_000_000 // 50 trillion
const MAX_ANNUAL_RATE = 1000 // 1,000%

export default function CompoundInterestCalculator() {
const [initialAmount, setInitialAmount] = useState<string>("")
const [annualRate, setAnnualRate] = useState<string>("")
const [periods, setPeriods] = useState<string>("")
const [selectedCompounding, setSelectedCompounding] = useState<CompoundingPeriod>("monthly")

const principal = parseFloat(initialAmount.replace('$', '')) || 0
const rate = (parseFloat(annualRate.replace('%', '')) || 0) / 100
const principal = parseFloat(initialAmount) || 0
const rate = (parseFloat(annualRate) || 0) / 100
const totalPeriods = parseFloat(periods) || 0

const selectedOption = useMemo(() =>
const selectedOption = useMemo(() =>
compoundingOptions.find((o) => o.value === selectedCompounding)!,
[selectedCompounding]
)
Expand All @@ -71,94 +74,193 @@ export default function CompoundInterestCalculator() {
}
})
}, [principal, rate, totalPeriods, selectedOption.periodsPerYear])


const [initialAmountError, setInitialAmountError] = useState<string>("")
const [annualRateError, setAnnualRateError] = useState<string>("")

type CompoundingPeriod = 'daily' | 'weekly' | 'biweekly' | 'monthly' | 'quarterly' | 'semi-annually' | 'annually';

const getPeriodText = (compounding: CompoundingPeriod, periods: number): string => {
const periodMap: Record<CompoundingPeriod, [string, string]> = {
daily: ['day', 'days'],
weekly: ['week', 'weeks'],
biweekly: ['bi-weekly period', 'bi-weekly periods'],
monthly: ['month', 'months'],
quarterly: ['quarter', 'quarters'],
'semi-annually': ['semi-annual period', 'semi-annual periods'],
annually: ['year', 'years']
};
const getPeriodText = (compounding: CompoundingPeriod, periods: number): string => {
const periodMap: Record<CompoundingPeriod, [string, string]> = {
daily: ['day', 'days'],
weekly: ['week', 'weeks'],
biweekly: ['bi-weekly period', 'bi-weekly periods'],
monthly: ['month', 'months'],
quarterly: ['quarter', 'quarters'],
'semi-annually': ['semi-annual period', 'semi-annual periods'],
annually: ['year', 'years']
};

const [singular, plural] = periodMap[compounding];
return periods === 1 ? singular : plural;
};
const [singular, plural] = periodMap[compounding];
return periods === 1 ? singular : plural;
};

return (
<div className=" p-6 max-w-5xl mx-auto">
<div className="p-6 max-w-5xl mx-auto">
<div className="max-w-6xl mx-auto">
{/* Header */}
<h1 className="sr-only mb-2">Compounding Frequency Calculator</h1>
<h1 className="sr-only">Compounding Frequency Calculator</h1>
<ThemeToggle />
<div className="flex flex-col md:flex-row gap-8">

{/* Input Fields */}
<section className="space-y-6 mb-10 w-full lg:w-1/2">
<section
aria-label="Calculator inputs"
className="space-y-6 mb-10 w-full lg:w-1/2"
>
<div>
<label className="block font-semibold text-foreground mb-2">Initial amount</label>
<label
htmlFor="initial-amount"
className="block font-semibold text-foreground mb-2"
>
Initial amount
</label>
<div className="relative">
<Input
id="initial-amount"
type="text"
value={initialAmount}
onChange={(e) => {
const input = e.target.value;
const numericPart = input.replace(/^\$/, '').replace(/[^0-9.]/g, '');
setInitialAmount('$' + numericPart);
const numericPart = input.replace(/[^0-9.]/g, "");
const numericValue = parseFloat(numericPart);
if (
!isNaN(numericValue) &&
numericValue > MAX_INITIAL_AMOUNT
) {
setInitialAmountError(
"Initial amount cannot exceed $50,000,000,000,000.",
);
return;
}
setInitialAmountError("");
setInitialAmount(numericPart);
}}
className="font-bold block w-full rounded-md shadow-sm py-2 px-3 border pr-10 [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none"
min="0"
className={`block w-full pl-8 rounded-md shadow-sm border [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none ${initialAmountError ? "border-[var(--color-inline-error)] border-2" : ""}`}
/>
<span className="absolute left-4 top-1/2 -translate-y-1/2 text-[var(--color-symbols)]">
$
</span>
</div>
{initialAmountError && (
<p
role="alert"
className="mt-1 text-sm text-[var(--color-inline-error)] font-semibold"
>
{initialAmountError}
</p>
)}
</div>

<div>
<label className="block font-semibold text-foreground mb-2">Annual interest rate</label>
<label
htmlFor="annual-rate"
className="block font-semibold text-foreground mb-2"
>
Annual interest rate
</label>
<div className="relative">
<Input
id="annual-rate"
type="text"
value={annualRate}
onChange={(e) => {
const input = e.target.value;
const numericPart = input.replace(/^%/, '').replace(/[^0-9.]/g, '');
setAnnualRate(numericPart + '%');
const numericPart = input.replace(/[^0-9.]/g, "");
const numericValue = parseFloat(numericPart);
if (
!isNaN(numericValue) &&
numericValue > MAX_ANNUAL_RATE
) {
setAnnualRateError(
"Annual interest rate cannot exceed 1,000%.",
);
return;
}
setAnnualRateError("");
setAnnualRate(numericPart);
}}
className="font-bold block w-full rounded-md shadow-sm py-2 px-3 border pr-10 [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none"
className={`block w-full rounded-md shadow-sm py-2 px-3 border pr-10 [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none ${annualRateError ? "border-[var(--color-inline-error)] border-2" : ""}`}
min="0"
step="0.1"
/>
<span
aria-hidden="true"
className="absolute right-3 top-1/2 -translate-y-1/2 font-medium text-[var(--color-symbols)]"
>
%
</span>
</div>
{annualRateError && (
<p
role="alert"
className="mt-1 text-sm text-[var(--color-inline-error)] font-semibold"
>
{annualRateError}
</p>
)}
</div>

<div>
<div className="flex items-start gap-2">
<label className="block font-semibold text-foreground mb-2">Number of compounding periods</label>
<InfoPopover title="Number of compounding periods">Periods are counted based on the selected compounding frequency. For monthly compounding, 60 periods equals 60 months.</InfoPopover>
<label
htmlFor="periods"
className="block font-semibold text-foreground mb-2"
>
Number of compounding periods
</label>
<InfoPopover title="Number of compounding periods">
Periods are counted based on the selected compounding
frequency. For monthly compounding, 60 periods equals 60
months.
</InfoPopover>
</div>
<div className="relative">
<Input
id="periods"
type="number"
value={periods}
onChange={(e) => setPeriods(e.target.value)}
className="font-bold block w-full rounded-md shadow-sm py-2 px-3 border pr-10 [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none"
onChange={(e) => {
const val = e.target.value;
if (val === "" || Number(val) >= 0) setPeriods(val);
}}
onKeyDown={(e) => {
if (e.key === "-" || e.key === "e") e.preventDefault();
}}
onBlur={() => {
if (periods.startsWith(".")) {
setPeriods("0" + periods);
}
}}
aria-describedby="periods-info"
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Collaborator

@imonroe imonroe May 22, 2026

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periods-info isn't an id that's in the page.

className="block w-full rounded-md shadow-sm py-2 px-3 border pr-10 [appearance:textfield] [&::-webkit-outer-spin-button]:appearance-none [&::-webkit-inner-spin-button]:appearance-none"
min="0"
/>
</div>
</div>

<div>
<div className="flex items-start gap-2">
<label className="block font-semibold text-foreground mb-3">Compounding frequency</label>
<InfoPopover title="Compounding frequency">Compounding frequency is how often interest is calculated and added to the balance. For example, monthly compounding applies interest once each month.</InfoPopover>
<label
htmlFor="compounding-frequency"
className="block font-semibold text-foreground mb-3"
>
Compounding frequency
</label>
<InfoPopover title="Compounding frequency">
Compounding frequency is how often interest is calculated and
added to the balance. For example, monthly compounding applies
interest once each month.
</InfoPopover>
</div>
<div className="flex items-center gap-2">
<select
id="compounding-frequency"
value={selectedCompounding}
onChange={(e) => setSelectedCompounding(e.target.value as CompoundingPeriod)}
onChange={(e) =>
setSelectedCompounding(e.target.value as CompoundingPeriod)
}
aria-describedby="compounding-frequency-info"
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@imonroe imonroe May 22, 2026

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compounding-frequency-info isn't an id on the page.

className="border-1 w-full rounded-md shadow-sm py-2 px-3 appearance-none"
>
{compoundingOptions.map((option) => (
Expand All @@ -167,7 +269,10 @@ const getPeriodText = (compounding: CompoundingPeriod, periods: number): string
</option>
))}
</select>
<div className="pointer-events-none ml-[-40px] text-gray-400 text-lg">
<div
className="pointer-events-none ml-[-40px] text-gray-400 text-lg"
aria-hidden="true"
>
<FaAngleDown />
</div>
</div>
Expand All @@ -177,59 +282,113 @@ const getPeriodText = (compounding: CompoundingPeriod, periods: number): string
{/* Results Section */}
<Card className="w-full lg:w-1/2 bg-[var(--card-background)] rounded-3xl p-[32px]">
<CardContent className="p-0">
<p className="text-[20px] font-bold mb-1">
Balance after {periods} {getPeriodText(selectedCompounding, Number(periods))}
</p>
<h2 className="text-[20px] font-bold mb-1">
Balance after {periods}{" "}
{getPeriodText(selectedCompounding, Number(periods))}
</h2>
<p className="text-3xl font-bold text-lagunita mb-5">
{formatCurrency(selectedResult.finalAmount)}</p>
{formatCurrency(selectedResult.finalAmount)}
</p>
<p className="text-[16px] font-semibold mb-1">
Interest accrued over {periods} {getPeriodText(selectedCompounding, Number(periods))}
Interest accrued over {periods}{" "}
{getPeriodText(selectedCompounding, Number(periods))}
</p>
<p className="text-3xl font-bold text-foreground">
{formatCurrency(selectedResult.interestEarned)}
</p>
<p className="text-[16px] font-semibold text-foreground">
With <span className="text-lagunita">{selectedCompounding === 'semi-annually' ? 'semi-annual' : selectedCompounding === 'annually' ? 'annual' : selectedCompounding}</span> compounding
With{" "}
<span className="text-lagunita">
{selectedCompounding === "semi-annually"
? "semi-annual"
: selectedCompounding === "annually"
? "annual"
: selectedCompounding}
</span>{" "}
compounding
</p>
</CardContent>
</Card>
</div>
{/* Comparison Table */}
<section className="rounded-3xl bg-[var(--grey-background)] p-6 mt-10">
<h2 className="text-xl font-semibold mb-2">Comparison Across Compounding Frequencies</h2>

{/* Comparison Table */}
<section
aria-label="Comparison across compounding frequencies"
className="rounded-3xl bg-[var(--grey-background)] p-6 mt-10"
>
<h2 className="text-xl font-semibold mb-2">
Comparison Across Compounding Frequencies
</h2>
<p className="text-sm mb-4">
See how compounding frequency affects returns over the same time period.
See how compounding frequency affects returns over the same time
period.
</p>

<div className="overflow-hidden bg-card">
<table className="min-w-full">
<thead>
<tr>
<th className="font-semibold text-left px-4 py-3">Compounding Frequency</th>
<th className="font-semibold text-right px-4 py-3">Number of <br/>Compounding Periods</th>
<th className="font-semibold text-right px-4 py-3">Final Amount</th>
<th className="font-semibold text-right px-4 py-3">Interest Accrued</th>
<th scope="col" className="font-semibold text-left px-4 py-3">
Compounding Frequency
</th>
<th
scope="col"
className="font-semibold text-right px-4 py-3"
>
Number of <br />
Compounding Periods
</th>
<th
scope="col"
className="font-semibold text-right px-4 py-3"
>
Final Amount
</th>
<th
scope="col"
className="font-semibold text-right px-4 py-3"
>
Interest Accrued
</th>
</tr>
</thead>
<tbody>
{comparisonResults.map((result) => (
<tr
key={result.value}
className={selectedCompounding === result.value ? "bg-lagunita-lighter text-lagunita font-bold" : ""}
aria-current={
selectedCompounding === result.value ? "true" : undefined
}
className={
selectedCompounding === result.value
? "bg-[var(--grey-background)] text-[var(--color-teal)] font-bold"
: ""
}
>
<td className="px-4 py-3 border-b">{result.label}</td>
<td className="text-right px-4 py-3 border-b text-foreground">{Number(result.totalPeriods.toFixed(2))}</td>
<td className="text-right px-4 py-3 border-b text-foreground">{formatCurrency(result.finalAmount)}</td>
<td className="text-right px-4 py-3 border-b">{formatCurrency(result.interestEarned)}</td>
<td className="text-right px-4 py-3 border-b">
{result.totalPeriods % 1 === 0
? result.totalPeriods.toFixed(0)
: result.totalPeriods.toFixed(2)}
</td>
<td className="text-right px-4 py-3 border-b">
{formatCurrency(result.finalAmount)}
</td>
<td className="text-right px-4 py-3 border-b">
{formatCurrency(result.interestEarned)}
</td>
</tr>
))}
</tbody>
</table>
<p className="pt-3 font-bold text-sm">Over the same time period, more frequent compounding generally results in more interest accrued, assuming the annual interest rate stays the same.</p>
<p className="pt-3 font-bold text-sm">
Over the same time period, more frequent compounding results in
more interest accrued, assuming the annual interest rate stays the
same.
</p>
</div>
</section>

</div>
</div>
)
);
}
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