This calculator emulates the Time Value of Money (TVM) functions of the HP 10bII+ financial calculator. Input four of the five TVM variables (N, I/YR, PV, PMT, FV) and solve for the fifth.
Cash Flow Convention: Enter cash outflows (money paid) as negative numbers and cash inflows (money received) as positive numbers. For example, if you are saving, your initial deposit (PV) or regular payments (PMT) would be negative, and your future savings (FV) would be positive.
function toggleInput(solveFor) {
var inputs = ['inputN', 'inputIYR', 'inputPV', 'inputPMT', 'inputFV'];
for (var i = 0; i < inputs.length; i++) {
var inputElement = document.getElementById(inputs[i]);
inputElement.disabled = false;
inputElement.classList.remove('disabled-input');
}
var solveInputId = 'input' + solveFor.replace('/', ''); // e.g., inputIYR
var elementToDisable = document.getElementById(solveInputId);
if (elementToDisable) {
elementToDisable.disabled = true;
elementToDisable.value = ''; // Clear value when disabled
elementToDisable.classList.add('disabled-input');
}
document.getElementById("result").innerHTML = ""; // Clear previous result
}
// Initialize disabled state on load
window.onload = function() {
toggleInput(document.querySelector('input[name="solveFor"]:checked').value);
};
function calculateTVM() {
var solveFor = document.querySelector('input[name="solveFor"]:checked').value;
var N_val = parseFloat(document.getElementById('inputN').value);
var IYR_val = parseFloat(document.getElementById('inputIYR').value);
var PV_val = parseFloat(document.getElementById('inputPV').value);
var PMT_val = parseFloat(document.getElementById('inputPMT').value);
var FV_val = parseFloat(document.getElementById('inputFV').value);
var periodsPerYear = parseFloat(document.getElementById('periodsPerYear').value);
var paymentTiming = parseFloat(document.querySelector('input[name="paymentTiming"]:checked').value); // 0 for End, 1 for Begin
var resultDiv = document.getElementById('result');
resultDiv.className = 'result-container'; // Reset class
// Validate inputs
var inputsValid = true;
var errorMessages = [];
if (solveFor !== 'N' && (isNaN(N_val) || N_val < 0)) { // N can be 0 for some calculations, but usually positive
errorMessages.push("Number of Periods (N) must be a non-negative number.");
inputsValid = false;
}
if (solveFor !== 'I/YR' && isNaN(IYR_val)) {
errorMessages.push("Interest Rate per Year (I/YR) must be a number.");
inputsValid = false;
}
if (solveFor !== 'PV' && isNaN(PV_val)) {
errorMessages.push("Present Value (PV) must be a number.");
inputsValid = false;
}
if (solveFor !== 'PMT' && isNaN(PMT_val)) {
errorMessages.push("Payment (PMT) must be a number.");
inputsValid = false;
}
if (solveFor !== 'FV' && isNaN(FV_val)) {
errorMessages.push("Future Value (FV) must be a number.");
inputsValid = false;
}
if (!inputsValid) {
resultDiv.innerHTML = "Error:" + errorMessages.join("");
resultDiv.classList.add('error');
return;
}
// Convert annual rate to periodic rate and N to total periods
var i_per_period = (IYR_val / 100) / periodsPerYear;
var n_total_periods = N_val * periodsPerYear;
var calculatedValue;
var resultUnit = "";
// Helper function for TVM equation (used for I/YR solver)
// f(i_per_period) = PV * (1 + i_per_period)^n_total_periods + PMT * (((1 + i_per_period)^n_total_periods – 1) / i_per_period) * (1 + i_per_period * paymentTiming) + FV
function calculateTVM_equation(pv, pmt, fv, n, i, type) {
if (n === 0) { // If no periods, PV + FV + PMT = 0 (if PMT is also 0)
return pv + fv; // PMT is irrelevant if n=0
}
if (i === 0) {
return pv + pmt * n * (1 + type) + fv; // Simplified for i=0
}
var term1 = pv * Math.pow(1 + i, n);
var term2 = pmt * ((Math.pow(1 + i, n) – 1) / i) * (1 + i * type);
return term1 + term2 + fv;
}
switch (solveFor) {
case 'N':
if (i_per_period === 0) {
if (PMT_val * (1 + paymentTiming) === 0) {
calculatedValue = (PV_val + FV_val === 0) ? 0 : NaN; // If PMT is 0 and i is 0, PV+FV must be 0.
} else {
calculatedValue = (-FV_val – PV_val) / (PMT_val * (1 + paymentTiming));
}
} else {
var term_pmt_factor = (1 + i_per_period * paymentTiming) / i_per_period;
var numerator = PMT_val * term_pmt_factor – FV_val;
var denominator = PV_val + PMT_val * term_pmt_factor;
if (denominator === 0) { // Avoid division by zero
calculatedValue = NaN;
} else {
var ratio = numerator / denominator;
if (ratio <= 0) { // Logarithm of non-positive number is undefined
calculatedValue = NaN;
} else {
calculatedValue = Math.log(ratio) / Math.log(1 + i_per_period);
}
}
}
calculatedValue = calculatedValue / periodsPerYear; // Convert total periods back to N (years/original periods)
resultUnit = " periods";
break;
case 'I/YR':
var low = -0.99; // -99% periodic rate
var high = 10; // 1000% periodic rate
var iterations = 200; // Sufficient for good precision
var current_i = 0;
var f_low, f_high, f_mid;
// Check for trivial case where I/YR is 0
if (Math.abs(calculateTVM_equation(PV_val, PMT_val, FV_val, n_total_periods, 0, paymentTiming)) 0) { // No root found in the initial range, or multiple roots
calculatedValue = NaN; // Indicate no solution in this range
} else {
for (var iter = 0; iter < iterations; iter++) {
current_i = (low + high) / 2;
f_mid = calculateTVM_equation(PV_val, PMT_val, FV_val, n_total_periods, current_i, paymentTiming);
if (Math.abs(f_mid) < 0.0000001) { // Check for convergence
break;
}
if (f_low * f_mid < 0) { // Root is between low and mid
high = current_i;
} else { // Root is between mid and high
low = current_i;
f_low = f_mid; // Update f_low to f_mid for next iteration
}
}
calculatedValue = current_i * periodsPerYear * 100; // Convert periodic rate to annual percentage
}
}
resultUnit = "%";
break;
case 'PV':
if (i_per_period === 0) {
calculatedValue = -FV_val – PMT_val * n_total_periods * (1 + paymentTiming);
} else {
var term_pmt = PMT_val * ((Math.pow(1 + i_per_period, n_total_periods) – 1) / i_per_period) * (1 + i_per_period * paymentTiming);
calculatedValue = (-FV_val – term_pmt) / Math.pow(1 + i_per_period, n_total_periods);
}
resultUnit = "$";
break;
case 'PMT':
if (i_per_period === 0) {
if (n_total_periods * (1 + paymentTiming) === 0) {
calculatedValue = NaN; // Cannot solve if no periods or payment timing factor is 0
} else {
calculatedValue = (-FV_val – PV_val) / (n_total_periods * (1 + paymentTiming));
}
} else {
var term_numerator = -FV_val – PV_val * Math.pow(1 + i_per_period, n_total_periods);
var term_denominator = ((Math.pow(1 + i_per_period, n_total_periods) – 1) / i_per_period) * (1 + i_per_period * paymentTiming);
if (term_denominator === 0) {
calculatedValue = NaN; // Avoid division by zero
} else {
calculatedValue = term_numerator / term_denominator;
}
}
resultUnit = "$";
break;
case 'FV':
if (i_per_period === 0) {
calculatedValue = -PV_val – PMT_val * n_total_periods * (1 + paymentTiming);
} else {
var term_pv = PV_val * Math.pow(1 + i_per_period, n_total_periods);
var term_pmt = PMT_val * ((Math.pow(1 + i_per_period, n_total_periods) – 1) / i_per_period) * (1 + i_per_period * paymentTiming);
calculatedValue = -term_pv – term_pmt;
}
resultUnit = "$";
break;
}
if (isNaN(calculatedValue) || !isFinite(calculatedValue)) {
resultDiv.innerHTML = "Error: Cannot calculate. Please check your inputs for logical consistency (e.g., trying to solve for N with conflicting cash flows, or I/YR with no change in value).";
resultDiv.classList.add('error');
} else {
var formattedValue = calculatedValue.toFixed(4); // Format to 4 decimal places for precision
if (resultUnit === "$") {
formattedValue = parseFloat(formattedValue).toLocaleString('en-US', { style: 'currency', currency: 'USD', minimumFractionDigits: 2, maximumFractionDigits: 2 });
} else if (resultUnit === "%") {
formattedValue = parseFloat(formattedValue).toFixed(4); // Keep 4 decimal places for percentage
} else { // For N
formattedValue = parseFloat(formattedValue).toFixed(4);
}
resultDiv.innerHTML = "" + solveFor + " = " + formattedValue + resultUnit + "";
}
}
About the HP 10bII+ Financial Calculator
The HP 10bII+ is a popular financial calculator known for its ease of use and powerful Time Value of Money (TVM) functions. It's widely used by students and professionals in finance, accounting, and real estate.
The core of its functionality revolves around five key variables:
N (Number of Periods): The total number of compounding or payment periods.
I/YR (Interest Rate per Year): The annual interest rate, entered as a percentage.
PV (Present Value): The current value of a future sum of money or stream of cash flows.
PMT (Payment): The amount of each regular payment in an annuity.
FV (Future Value): The value of an asset or cash at a specified date in the future.
This web-based emulator allows you to perform the same TVM calculations by inputting four known variables and solving for the fifth, just like the physical HP 10bII+ calculator. It also includes options for adjusting the number of periods per year (P/YR) and payment timing (End/Begin of period), which are crucial settings on the actual device.
Example Usage:
Scenario 1: Saving for a Future Goal (Solve for FV)
You deposit $10,000 today (PV = -10000) into an account earning 5% annual interest (I/YR = 5). You also plan to deposit an additional $200 at the end of each month (PMT = -200) for 10 years (N = 10). Payments are monthly (P/YR = 12) at the end of the period. How much will you have in 10 years?
Select "Solve For: FV"
N: 10
I/YR: 5
PV: -10000
PMT: -200
P/YR: 12 (Monthly)
Payment Timing: End of Period
Result (FV): ~$47,940.00
Scenario 2: Loan Payment Calculation (Solve for PMT)
You want to take out a $200,000 mortgage (PV = 200000) at an annual interest rate of 4% (I/YR = 4) over 30 years (N = 30). Payments are monthly (P/YR = 12) at the end of the period, and you want to pay off the loan completely (FV = 0). What will your monthly payment be?
Select "Solve For: PMT"
N: 30
I/YR: 4
PV: 200000
FV: 0
P/YR: 12 (Monthly)
Payment Timing: End of Period
Result (PMT): ~$-954.83 (The negative sign indicates an outflow/payment)