Google Sheets Apps Script for getting the Net Asset Value (NAV) of any instrument by (ISIN, date) using the Yahoo Finance API

getFundNAV.gs

function getFundNAV(isin, date) {

  // 0. Initial date validation
  const targetDate = new Date(date);
  if (isNaN(targetDate.getTime())) return 'Invalid date';
  if (targetDate > new Date()) return 'Date is in the future';

  // 1. Get Yahoo Finance symbol from ISIN
  const searchUrl = `https://query2.finance.yahoo.com/v1/finance/search?q=${isin}`;
  const searchResp = UrlFetchApp.fetch(searchUrl);
  const searchData = JSON.parse(searchResp.getContentText());
  const symbol = searchData.quotes?.[0]?.symbol;
  if (!symbol) return 'No Yahoo Finance symbol found for the provided ISIN';

  // 2. Convert target date to timestamps (get until 30 days before requested date)
  const to_date = Math.floor(targetDate.getTime() / 1000) + 86400;
  const from_date = to_date - 86400 * 30;

  // 3. Retrieve historical NAV data from Yahoo Finance
  const chartUrl = `https://query2.finance.yahoo.com/v8/finance/chart/${symbol}?period1=${from_date}&period2=${to_date}&interval=1d`;
  const chartResp = UrlFetchApp.fetch(chartUrl);
  const chartData = JSON.parse(chartResp.getContentText());
  if (chartData.chart.error) return 'Yahoo Finance error: ' + chartData.chart.error.description;

  // 4. Data extraction (timestamps and corresponding NAVs)
  const timestamps = chartData.chart.result?.[0]?.timestamp;
  const navs = chartData.chart.result?.[0]?.indicators?.quote?.[0]?.close;
  if (!timestamps || !navs) return 'Historical NAV data is not available';

  // 4. Find most recent NAV on or before the requested date
  for (let i = timestamps.length - 1; i >= 0; i--) {
    if (timestamps[i] * 1000 <= targetDate.getTime() && navs[i] !== null)
      return navs[i];
  }

  return 'Net Asset Value not found for the requested or previous dates';
}

/* Example API calls (for, e.g., Vanguard S&P 500 ETF):
*  https://query2.finance.yahoo.com/v1/finance/search?q=IE00BFMXXD54
*  https://query2.finance.yahoo.com/v8/finance/chart/VOO?period1=1745193600&period2=1745280000&interval=1d
*/

/* Example of use in any Google Sheets spreadsheet:
*  1. Extensions > Apps script 
*  2. "Add new file" and copy-paste the function
*  3. Back to the spreadsheet, use the function in any cell like '=getFundNAV("IE00BFMXXD54", "2025-04-22")', e.g.,
*     to pull the NAV on close time for the Vanguard S&P 500 ETF (ISIN "IE00BFMXXD54") on 2025 Apr 22nd.
*  4. Enjoy ;)
*/