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Time Value of Money client feedback updates #122

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Time Value of Money client feedback updates #122

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67ed153
Time Value of Money client feedback updates
jenbreese Jun 8, 2026
c43cce1
Fixups to questions and added errors
jenbreese Jun 9, 2026
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77 changes: 55 additions & 22 deletions app/interactives/time-value-money-calculator/app.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,7 @@ export function TVMCalculator() {
const [result, setResult] = useState<number | null>(null)
const [calcError, setCalcError] = useState<string>("")
const [fieldErrors, setFieldErrors] = useState<FieldError[]>([])
const [signError, setSignError] = useState<string>("")
const [showHowToUse, setShowHowToUse] = useState<boolean>(false)
const [showExamples, setShowExamples] = useState<boolean>(false)
const [exampleMode, setExampleMode] = useState<"saving" | "borrowing">("saving")
Expand Down Expand Up @@ -149,8 +150,11 @@ export function TVMCalculator() {
const getFieldError = (field: string): string | undefined =>
fieldErrors.find(e => e.field === field)?.message

const displayError = calcError || signError

const calculate = useCallback(() => {
setCalcError("")
setSignError("")

// ── Don't calculate (or show errors) until all required fields are filled ──
const requiredFields: Record<SolveFor, string[]> = {
Expand Down Expand Up @@ -189,6 +193,19 @@ export function TVMCalculator() {
const timingMultiplier = paymentTiming === "beginning" ? (1 + ratePerPeriod) : 1

try {
// Require opposite signs for RATE/NPER solves: at least one cash flow must have opposite sign
if ((solveFor === "RATE" || solveFor === "NPER")) {
const allPositive = pv > 0 && pmt > 0 && fv > 0
const allNegative = pv < 0 && pmt < 0 && fv < 0
if (allPositive || allNegative) {
const which = solveFor === "RATE" ? "rate" : "number of periods"
setSignError(
`These values can't be solved. To find the ${which}, money paid out and money received need opposite signs — for example, enter what you invest as negative and what you receive as positive.`
)
setResult(null)
return
}
}
let calculatedValue: number

switch (solveFor) {
Expand Down Expand Up @@ -264,10 +281,24 @@ export function TVMCalculator() {
case "NPER": {
if (ratePerPeriod === 0) {
if (pmt === 0 && payment === "0") throw new Error("Payment cannot be 0 when rate is 0")
calculatedValue = pmt === 0 ? 0 : -(pv + fv) / pmt
const calculatedNper = pmt === 0 ? 0 : -(pv + fv) / pmt
if (!isFinite(calculatedNper) || calculatedNper <= 0) {
throw new Error("These payments are too small to reach this future value. Try a larger payment, a higher rate, or a lower target.")
}
calculatedValue = calculatedNper
} else {
const pmtAdj = pmt * timingMultiplier
calculatedValue = Math.log((pmtAdj - fv * ratePerPeriod) / (pmtAdj + pv * ratePerPeriod)) / Math.log(1 + ratePerPeriod)
const numerator = pmtAdj - fv * ratePerPeriod
const denominator = pmtAdj + pv * ratePerPeriod
const ratio = numerator / denominator
if (ratio <= 0) {
throw new Error("These payments are too small to reach this future value. Try a larger payment, a higher rate, or a lower target.")
}
const calculatedNper = Math.log(ratio) / Math.log(1 + ratePerPeriod)
if (!isFinite(calculatedNper) || calculatedNper <= 0) {
throw new Error("These payments are too small to reach this future value. Try a larger payment, a higher rate, or a lower target.")
}
calculatedValue = calculatedNper
}
break
}
Expand Down Expand Up @@ -433,7 +464,8 @@ export function TVMCalculator() {
fv: "30000",
rate: "3.5",
compoundFreq: "12",
paymentFreq: "12",
paymentFreqMode: "different" as PaymentFrequencyMode,
paymentFreq: "26",
},
};
}
Expand Down Expand Up @@ -518,7 +550,7 @@ export function TVMCalculator() {
"Number of Periods Example: Solve for time to pay off credit card",
bullets: [
"Present value (credit card balance): positive",
"Payment per period (monthly payments): negative",
"Payment per period (bi-weekly payments): negative",
"Future value (remaining balance): zero",
],
example: {
Expand All @@ -528,7 +560,7 @@ export function TVMCalculator() {
fv: "0",
rate: "18",
compoundFreq: "365",
paymentFreq: "12",
paymentFreq: "26",
paymentFreqMode: "different" as PaymentFrequencyMode,
},
};
Expand Down Expand Up @@ -566,8 +598,8 @@ export function TVMCalculator() {
</button>
{showExamples && (
<div className="ml-4 pl-4 border-l-2 border-border/50 space-y-4">
<div className="flex items-center text-xs">
<span className=" mr-1">I am:</span>
<div className="flex items-center text-sm">
<span className="mr-1">I am:</span>
{(["saving", "borrowing"] as const).map(mode => (
<button
key={mode}
Expand All @@ -576,10 +608,10 @@ export function TVMCalculator() {
setExampleMode(mode)
setPresentValue(""); setFutureValue(""); setPayment(""); setAnnualRate(""); setPeriods("")
}}
className={`px-1.5 py-0.5 rounded border transition-colors ${
className={`px-1.5 py-0.5 mr-2 rounded border transition-colors ${
exampleMode === mode
? "border-green-500 bg-green-500/10 text-green-600"
: "border-transparent hover:text-foreground"
? "border-[var(--color-navy)] bg-white text-[var(--color-navy)]"
: "border-white hover:underline hover:text-foreground"
}`}
>
{mode}
Expand Down Expand Up @@ -625,6 +657,7 @@ export function TVMCalculator() {
onClick={() => {
if (option.value !== solveFor) {
setPresentValue(""); setFutureValue(""); setPayment(""); setAnnualRate(""); setPeriods("")
setPaymentFrequencyMode("same")
}
setSolveFor(option.value)
}}
Expand Down Expand Up @@ -658,7 +691,7 @@ export function TVMCalculator() {
onBlur={(e) => handleInputBlur(e.target.value, setPresentValue)}
className={`border-border pl-7 bg-card ${getFieldError("presentValue") ? "border-destructive" : ""}`} />
</div>
{getFieldError("presentValue") && <p className="text-sm text-destructive">{getFieldError("presentValue")}</p>}
{getFieldError("presentValue") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("presentValue")}</p>}
</div>
)}

Expand All @@ -673,7 +706,7 @@ export function TVMCalculator() {
onBlur={(e) => handleInputBlur(e.target.value, setPayment)}
className={`border-border pl-7 bg-card ${getFieldError("payment") ? "border-destructive" : ""}`} />
</div>
{getFieldError("payment") && <p className="text-sm text-destructive">{getFieldError("payment")}</p>}
{getFieldError("payment") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("payment")}</p>}
</div>
)}

Expand All @@ -688,7 +721,7 @@ export function TVMCalculator() {
onBlur={(e) => handleInputBlur(e.target.value, setFutureValue)}
className={`border-border pl-7 bg-card ${getFieldError("futureValue") ? "border-destructive" : ""}`} />
</div>
{getFieldError("futureValue") && <p className="text-sm text-destructive">{getFieldError("futureValue")}</p>}
{getFieldError("futureValue") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("futureValue")}</p>}
</div>
)}

Expand All @@ -703,7 +736,7 @@ export function TVMCalculator() {
onBlur={(e) => handleInputBlur(e.target.value, setPayment)}
className={`border-border pl-7 bg-card ${getFieldError("payment") ? "border-destructive" : ""}`} />
</div>
{getFieldError("payment") && <p className="text-sm text-destructive">{getFieldError("payment")}</p>}
{getFieldError("payment") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("payment")}</p>}
</div>
)}

Expand All @@ -718,7 +751,7 @@ export function TVMCalculator() {
className={`border-border pr-8 bg-card ${getFieldError("annualRate") ? "border-destructive" : ""}`} />
<span className="absolute right-3 top-1/2 -translate-y-1/2">%</span>
</div>
{getFieldError("annualRate") && <p className="text-sm text-destructive">{getFieldError("annualRate")}</p>}
{getFieldError("annualRate") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("annualRate")}</p>}
</div>
)}

Expand All @@ -729,7 +762,7 @@ export function TVMCalculator() {
<Input id="periods" type="text" inputMode="numeric" value={periods}
onChange={(e) => { const val = e.target.value; if (val === "" || /^\d*$/.test(val)) setPeriods(val) }}
className={`border-border bg-card ${getFieldError("periods") ? "border-destructive" : ""}`} />
{getFieldError("periods") && <p className="text-sm text-destructive">{getFieldError("periods")}</p>}
{getFieldError("periods") && <p className="text-sm text-[var(--color-inline-error)]">{getFieldError("periods")}</p>}
</div>
)}

Expand Down Expand Up @@ -804,11 +837,11 @@ export function TVMCalculator() {
</section>

{/* Results Card */}
<Card className="w-full lg:w-1/2">
<Card className="w-full hidden md:block lg:w-1/2">
<CardContent className="w-full bg-[var(--card-background)] rounded-3xl p-[32px]">
<h2 className="text-[20px] font-bold mb-1">{currentOption?.label}</h2>
{calcError ? (
<p className="text-destructive font-medium text-lg">{calcError}</p>
{displayError ? (
<p className="text-[var(--color-inline-error)]">{displayError}</p>
) : result !== null ? (
<p className="text-3xl/normal font-bold text-[var(--color-teal)] mb-5 overflow-auto">{formatResult(result)}</p>
) : (
Expand All @@ -820,11 +853,11 @@ export function TVMCalculator() {

{/* Mobile sticky footer */}
<div className="md:hidden fixed bottom-0 left-0 right-0 bg-background border-t border-border p-4 shadow-lg">
<div className="flex items-center justify-between">
<div className="flex flex-col items-center justify-between">
<div>
<div className="text-xs ">{currentOption?.label}</div>
{calcError ? (
<p className="text-destructive font-medium">{calcError}</p>
{displayError ? (
<p className="text-[var(--color-inline-error)] font-medium">{displayError}</p>
) : result !== null ? (
<p className="text-2xl font-bold text-primary">{formatResult(result)}</p>
) : (
Expand Down