diff --git a/apps/api/src/app/core/current-rate.service.spec.ts b/apps/api/src/app/core/current-rate.service.spec.ts
new file mode 100644
index 000000000..905701c6d
--- /dev/null
+++ b/apps/api/src/app/core/current-rate.service.spec.ts
@@ -0,0 +1,60 @@
+import { CurrentRateService } from '@ghostfolio/api/app/core/current-rate.service';
+import { Currency } from '@prisma/client';
+import { ExchangeRateDataService } from '@ghostfolio/api/services/exchange-rate-data.service';
+import { PrismaService } from '@ghostfolio/api/services/prisma.service';
+
+jest.mock('../../services/exchange-rate-data.service', () => {
+  return {
+    // eslint-disable-next-line @typescript-eslint/naming-convention
+    exchangeRateDataService: jest.fn().mockImplementation(() => {
+      return {
+        toCurrency: (aValue: number,
+                     aFromCurrency: Currency,
+                     aToCurrency: Currency) => {
+          return 1 * aValue;
+        }
+      }
+    })
+  };
+});
+
+// https://jestjs.io/docs/manual-mocks#mocking-node-modules
+// jest.mock('?', () => {
+//   return {
+//     // eslint-disable-next-line @typescript-eslint/naming-convention
+//     prismaService: jest.fn().mockImplementation(() => {
+//       return {
+//         marketData: {
+//           findFirst: (data: any) => {
+//             return {
+//               marketPrice: 100
+//             };
+//           }
+//         }
+//       };
+//     })
+//   };
+// });
+
+xdescribe('CurrentRateService', () => {
+
+  let exchangeRateDataService: ExchangeRateDataService;
+  let prismaService: PrismaService;
+
+  beforeEach(() => {
+    exchangeRateDataService = new ExchangeRateDataService(undefined);
+    prismaService = new PrismaService();
+  });
+
+  it('getValue', () => {
+    const currentRateService = new CurrentRateService(exchangeRateDataService, prismaService);
+
+    expect(currentRateService.getValue({
+      date: new Date(),
+      symbol: 'AIA',
+      currency: Currency.USD,
+      userCurrency: Currency.CHF
+    })).toEqual(0);
+  });
+
+});
diff --git a/apps/api/src/app/core/current-rate.service.ts b/apps/api/src/app/core/current-rate.service.ts
new file mode 100644
index 000000000..fe1c470a6
--- /dev/null
+++ b/apps/api/src/app/core/current-rate.service.ts
@@ -0,0 +1,37 @@
+import { Currency } from '@prisma/client';
+import { PrismaService } from '@ghostfolio/api/services/prisma.service';
+import { ExchangeRateDataService } from '@ghostfolio/api/services/exchange-rate-data.service';
+
+export class CurrentRateService {
+
+  public constructor(
+    private readonly exchangeRateDataService: ExchangeRateDataService,
+    private prisma: PrismaService
+  ) {}
+
+  /**
+   * TODO: @dtslvr
+   */
+  public async getValue({date, symbol, currency, userCurrency}: GetValueParams): Promise<number> {
+    const marketData = await this.prisma.marketData.findFirst({
+      select: { date: true, marketPrice: true },
+      where: { date: date, symbol: symbol }
+    });
+
+    console.log(marketData); // { date: Date, marketPrice: number }
+
+    return this.exchangeRateDataService.toCurrency(
+      marketData.marketPrice,
+      currency,
+      userCurrency
+    );
+  }
+
+}
+
+export interface GetValueParams {
+  date: Date;
+  symbol: string;
+  currency: Currency;
+  userCurrency: Currency;
+}
diff --git a/apps/api/src/app/core/portfolio-calculator.spec.ts b/apps/api/src/app/core/portfolio-calculator.spec.ts
new file mode 100644
index 000000000..30b9fd693
--- /dev/null
+++ b/apps/api/src/app/core/portfolio-calculator.spec.ts
@@ -0,0 +1,459 @@
+import { PortfolioCalculator, PortfolioOrder } from '@ghostfolio/api/app/core/portfolio-calculator';
+import { CurrentRateService } from '@ghostfolio/api/app/core/current-rate.service';
+import { Currency } from '@prisma/client';
+import { OrderType } from '@ghostfolio/api/models/order-type';
+import Big from 'big.js';
+
+jest.mock('./current-rate.service.ts', () => {
+  return {
+    // eslint-disable-next-line @typescript-eslint/naming-convention
+    CurrentRateService: jest.fn().mockImplementation(() => {
+      return {
+        getValue: (date: Date, symbol: string, currency: Currency) => {
+          return 4;
+        }
+      };
+    })
+  };
+});
+
+describe('PortfolioCalculator', () => {
+
+  let currentRateService: CurrentRateService;
+  beforeEach(() => {
+    currentRateService = new CurrentRateService(null, null);
+  });
+
+  describe('calculate transaction points', () => {
+    it('with orders of only one symbol', () => {
+      const portfolioCalculator = new PortfolioCalculator(currentRateService, Currency.USD, ordersVTI);
+      const portfolioItemsAtTransactionPoints = portfolioCalculator.getPortfolioItemsAtTransactionPoints();
+
+      expect(portfolioItemsAtTransactionPoints).toEqual([
+        {
+          date: '2019-02-01',
+          items: [{
+            quantity: new Big('10'),
+            symbol: 'VTI',
+            investment: new Big('1443.8'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-08-03',
+          items: [{
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2020-02-02',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'VTI',
+            investment: new Big('652.55'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-02-01',
+          items: [{
+            quantity: new Big('15'),
+            symbol: 'VTI',
+            investment: new Big('2684.05'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-08-01',
+          items: [{
+            quantity: new Big('25'),
+            symbol: 'VTI',
+            investment: new Big('4460.95'),
+            currency: Currency.USD
+          }]
+        }
+      ]);
+    });
+
+    it('with two orders at the same day of the same type', () => {
+      const orders = [
+        ...ordersVTI,
+        {
+          date: '2021-02-01',
+          quantity: new Big('20'),
+          symbol: 'VTI',
+          type: OrderType.Buy,
+          unitPrice: new Big('197.15'),
+          currency: Currency.USD
+        }
+      ];
+      const portfolioCalculator = new PortfolioCalculator(currentRateService, Currency.USD, orders);
+      const portfolioItemsAtTransactionPoints = portfolioCalculator.getPortfolioItemsAtTransactionPoints();
+
+      expect(portfolioItemsAtTransactionPoints).toEqual([
+        {
+          date: '2019-02-01',
+          items: [{
+            quantity: new Big('10'),
+            symbol: 'VTI',
+            investment: new Big('1443.8'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-08-03',
+          items: [{
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2020-02-02',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'VTI',
+            investment: new Big('652.55'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-02-01',
+          items: [{
+            quantity: new Big('35'),
+            symbol: 'VTI',
+            investment: new Big('6627.05'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-08-01',
+          items: [{
+            quantity: new Big('45'),
+            symbol: 'VTI',
+            investment: new Big('8403.95'),
+            currency: Currency.USD
+          }]
+        }
+      ]);
+    });
+
+    it('with additional order', () => {
+      const orders = [
+        ...ordersVTI,
+        {
+          date: '2019-09-01',
+          quantity: new Big('5'),
+          symbol: 'AMZN',
+          type: OrderType.Buy,
+          unitPrice: new Big('2021.99'),
+          currency: Currency.USD
+        }
+      ];
+      const portfolioCalculator = new PortfolioCalculator(currentRateService, Currency.USD, orders);
+      const portfolioItemsAtTransactionPoints = portfolioCalculator.getPortfolioItemsAtTransactionPoints();
+
+      expect(portfolioItemsAtTransactionPoints).toEqual([
+        {
+          date: '2019-02-01',
+          items: [{
+            quantity: new Big('10'),
+            symbol: 'VTI',
+            investment: new Big('1443.8'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-08-03',
+          items: [{
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-09-01',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2020-02-02',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('5'),
+            symbol: 'VTI',
+            investment: new Big('652.55'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-02-01',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('15'),
+            symbol: 'VTI',
+            investment: new Big('2684.05'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-08-01',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('25'),
+            symbol: 'VTI',
+            investment: new Big('4460.95'),
+            currency: Currency.USD
+          }]
+        }
+      ]);
+    });
+
+    it('with additional buy & sell', () => {
+      const orders = [
+        ...ordersVTI,
+        {
+          date: '2019-09-01',
+          quantity: new Big('5'),
+          symbol: 'AMZN',
+          type: OrderType.Buy,
+          unitPrice: new Big('2021.99'),
+          currency: Currency.USD
+        },
+        {
+          date: '2020-08-02',
+          quantity: new Big('5'),
+          symbol: 'AMZN',
+          type: OrderType.Sell,
+          unitPrice: new Big('2412.23'),
+          currency: Currency.USD
+        }
+      ];
+      const portfolioCalculator = new PortfolioCalculator(currentRateService, Currency.USD, orders);
+      const portfolioItemsAtTransactionPoints = portfolioCalculator.getPortfolioItemsAtTransactionPoints();
+
+      expect(portfolioItemsAtTransactionPoints).toEqual([
+        {
+          date: '2019-02-01',
+          items: [{
+            quantity: new Big('10'),
+            symbol: 'VTI',
+            investment: new Big('1443.8'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-08-03',
+          items: [{
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2019-09-01',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('20'),
+            symbol: 'VTI',
+            investment: new Big('2923.7'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2020-02-02',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('5'),
+            symbol: 'VTI',
+            investment: new Big('652.55'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2020-08-02',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'VTI',
+            investment: new Big('652.55'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-02-01',
+          items: [{
+            quantity: new Big('15'),
+            symbol: 'VTI',
+            investment: new Big('2684.05'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2021-08-01',
+          items: [{
+            quantity: new Big('25'),
+            symbol: 'VTI',
+            investment: new Big('4460.95'),
+            currency: Currency.USD
+          }]
+        }
+      ]);
+    });
+
+    it('with mixed symbols', () => {
+      const portfolioCalculator = new PortfolioCalculator(currentRateService, Currency.USD, ordersMixedSymbols);
+      const portfolioItemsAtTransactionPoints = portfolioCalculator.getPortfolioItemsAtTransactionPoints();
+
+      expect(portfolioItemsAtTransactionPoints).toEqual([
+        {
+          date: '2017-01-03',
+          items: [{
+            quantity: new Big('50'),
+            symbol: 'TSLA',
+            investment: new Big('2148.5'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2017-07-01',
+          items: [{
+            quantity: new Big('0.5614682'),
+            symbol: 'BTCUSD',
+            investment: new Big('1999.9999999999998659756'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('50'),
+            symbol: 'TSLA',
+            investment: new Big('2148.5'),
+            currency: Currency.USD
+          }]
+        },
+        {
+          date: '2018-09-01',
+          items: [{
+            quantity: new Big('5'),
+            symbol: 'AMZN',
+            investment: new Big('10109.95'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('0.5614682'),
+            symbol: 'BTCUSD',
+            investment: new Big('1999.9999999999998659756'),
+            currency: Currency.USD
+          }, {
+            quantity: new Big('50'),
+            symbol: 'TSLA',
+            investment: new Big('2148.5'),
+            currency: Currency.USD
+          }]
+        }
+      ]);
+    });
+  });
+
+});
+
+const ordersMixedSymbols: PortfolioOrder[] = [
+  {
+    date: '2017-01-03',
+    quantity: new Big('50'),
+    symbol: 'TSLA',
+    type: OrderType.Buy,
+    unitPrice: new Big('42.97'),
+    currency: Currency.USD
+  },
+  {
+    date: '2017-07-01',
+    quantity: new Big('0.5614682'),
+    symbol: 'BTCUSD',
+    type: OrderType.Buy,
+    unitPrice: new Big('3562.089535970158'),
+    currency: Currency.USD
+  },
+  {
+    date: '2018-09-01',
+    quantity: new Big('5'),
+    symbol: 'AMZN',
+    type: OrderType.Buy,
+    unitPrice: new Big('2021.99'),
+    currency: Currency.USD
+  }
+];
+
+const ordersVTI: PortfolioOrder[] = [
+  {
+    date: '2019-02-01',
+    quantity: new Big('10'),
+    symbol: 'VTI',
+    type: OrderType.Buy,
+    unitPrice: new Big('144.38'),
+    currency: Currency.USD
+  },
+  {
+    date: '2019-08-03',
+    quantity: new Big('10'),
+    symbol: 'VTI',
+    type: OrderType.Buy,
+    unitPrice: new Big('147.99'),
+    currency: Currency.USD
+  },
+  {
+    date: '2020-02-02',
+    quantity: new Big('15'),
+    symbol: 'VTI',
+    type: OrderType.Sell,
+    unitPrice: new Big('151.41'),
+    currency: Currency.USD
+  },
+  {
+    date: '2021-08-01',
+    quantity: new Big('10'),
+    symbol: 'VTI',
+    type: OrderType.Buy,
+    unitPrice: new Big('177.69'),
+    currency: Currency.USD
+  },
+  {
+    date: '2021-02-01',
+    quantity: new Big('10'),
+    symbol: 'VTI',
+    type: OrderType.Buy,
+    unitPrice: new Big('203.15'),
+    currency: Currency.USD
+  }
+];
diff --git a/apps/api/src/app/core/portfolio-calculator.ts b/apps/api/src/app/core/portfolio-calculator.ts
new file mode 100644
index 000000000..4a10860e1
--- /dev/null
+++ b/apps/api/src/app/core/portfolio-calculator.ts
@@ -0,0 +1,154 @@
+import { Currency } from '@prisma/client';
+import { CurrentRateService } from '@ghostfolio/api/app/core/current-rate.service';
+import { OrderType } from '@ghostfolio/api/models/order-type';
+import Big from 'big.js';
+
+export class PortfolioCalculator {
+
+  private transactionPoints: TransactionPoint[];
+
+  constructor(
+    private currentRateService: CurrentRateService,
+    private currency: Currency,
+    orders: PortfolioOrder[]
+  ) {
+    this.computeTransactionPoints(orders);
+  }
+
+  addOrder(order: PortfolioOrder): void {
+
+  }
+
+  deleteOrder(order: PortfolioOrder): void {
+
+  }
+
+  getPortfolioItemsAtTransactionPoints(): TransactionPoint[] {
+    return this.transactionPoints;
+  }
+
+  getCurrentPositions(): { [symbol: string]: TimelinePosition } {
+    return {};
+  }
+
+  calculateTimeline(timelineSpecification: TimelineSpecification[], endDate: Date): TimelinePeriod[] {
+    return null;
+  }
+
+  private computeTransactionPoints(orders: PortfolioOrder[]) {
+    orders.sort((a, b) => a.date.localeCompare(b.date));
+
+    this.transactionPoints = [];
+    const symbols: { [symbol: string]: TransactionPointSymbol } = {};
+
+    let lastDate: string = null;
+    let lastTransactionPoint: TransactionPoint = null;
+    for (const order of orders) {
+      const currentDate = order.date;
+
+      let currentTransactionPointItem: TransactionPointSymbol;
+      const oldAccumulatedSymbol = symbols[order.symbol];
+
+      const factor = this.getFactor(order.type);
+      const unitPrice = new Big(order.unitPrice);
+      if (oldAccumulatedSymbol) {
+        currentTransactionPointItem = {
+          quantity: order.quantity.mul(factor).plus(oldAccumulatedSymbol.quantity),
+          symbol: order.symbol,
+          investment: unitPrice.mul(order.quantity).mul(factor).add(oldAccumulatedSymbol.investment),
+          currency: order.currency
+        };
+      } else {
+        currentTransactionPointItem = {
+          quantity: order.quantity.mul(factor),
+          symbol: order.symbol,
+          investment: unitPrice.mul(order.quantity).mul(factor),
+          currency: order.currency
+        };
+      }
+
+      symbols[order.symbol] = currentTransactionPointItem;
+
+      const items = lastTransactionPoint?.items ?? [];
+      const newItems = items.filter(transactionPointItem => transactionPointItem.symbol !== order.symbol);
+      if (!currentTransactionPointItem.quantity.eq(0)) {
+        newItems.push(currentTransactionPointItem);
+      } else {
+        delete symbols[order.symbol];
+      }
+      newItems.sort((a, b) => a.symbol.localeCompare(b.symbol));
+      if (lastDate !== currentDate || lastTransactionPoint === null) {
+        lastTransactionPoint = {
+          date: currentDate,
+          items: newItems
+        };
+        this.transactionPoints.push(lastTransactionPoint);
+      } else {
+        lastTransactionPoint.items = newItems;
+      }
+      lastDate = currentDate;
+    }
+  }
+
+  private getFactor(type: OrderType) {
+    let factor: number;
+    switch (type) {
+      case OrderType.Buy:
+        factor = 1;
+        break;
+      case OrderType.Sell:
+        factor = -1;
+        break;
+      default:
+        factor = 0;
+        break;
+    }
+    return factor;
+  }
+
+}
+
+interface TransactionPoint {
+  date: string;
+  items: TransactionPointSymbol[];
+}
+
+interface TransactionPointSymbol {
+  quantity: Big;
+  symbol: string;
+  investment: Big;
+  currency: Currency;
+}
+
+interface TimelinePosition {
+  averagePrice: Big;
+  firstBuyDate: string;
+  quantity: Big;
+  symbol: string;
+  investment: Big;
+  marketPrice: number;
+  transactionCount: number;
+}
+
+type Accuracy = 'year' | 'month' | 'day';
+
+interface TimelineSpecification {
+  start: Date;
+  accuracy: Accuracy
+}
+
+interface TimelinePeriod {
+  date: Date;
+  grossPerformance: number;
+  investment: number;
+  value: number;
+}
+
+export interface PortfolioOrder {
+  date: string;
+  quantity: Big;
+  symbol: string;
+  type: OrderType;
+  unitPrice: Big;
+  currency: Currency;
+}
diff --git a/package.json b/package.json
index 521bf25c5..c33634c9e 100644
--- a/package.json
+++ b/package.json
@@ -73,6 +73,7 @@
     "alphavantage": "2.2.0",
     "angular-material-css-vars": "2.1.0",
     "bent": "7.3.12",
+    "big.js": "^6.1.1",
     "bootstrap": "4.6.0",
     "cache-manager": "3.4.3",
     "cache-manager-redis-store": "2.0.0",
@@ -123,6 +124,7 @@
     "@nrwl/node": "12.5.4",
     "@nrwl/tao": "12.5.4",
     "@nrwl/workspace": "12.5.4",
+    "@types/big.js": "^6.1.1",
     "@types/cache-manager": "3.4.0",
     "@types/jest": "26.0.20",
     "@types/lodash": "4.14.168",
diff --git a/yarn.lock b/yarn.lock
index cf58770a9..edf8a2d9b 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2549,6 +2549,10 @@
   dependencies:
     "@babel/types" "^7.3.0"
 
+"@types/big.js@^6.1.1":
+  version "6.1.1"
+  integrity sha1-wr5egeDPDBwxcE47EvdQcS9kdBQ=
+
 "@types/body-parser@*":
   version "1.19.0"
   resolved "https://registry.yarnpkg.com/@types/body-parser/-/body-parser-1.19.0.tgz#0685b3c47eb3006ffed117cdd55164b61f80538f"
@@ -3943,6 +3947,10 @@ big.js@^5.2.2:
   resolved "https://registry.yarnpkg.com/big.js/-/big.js-5.2.2.tgz#65f0af382f578bcdc742bd9c281e9cb2d7768328"
   integrity sha512-vyL2OymJxmarO8gxMr0mhChsO9QGwhynfuu4+MHTAW6czfq9humCB7rKpUjDd9YUiDPU4mzpyupFSvOClAwbmQ==
 
+big.js@^6.1.1:
+  version "6.1.1"
+  integrity sha1-Y7NbGdyXdclJke5dt2lIgGVdVTc=
+
 bignumber.js@^9.0.1:
   version "9.0.1"
   resolved "https://registry.yarnpkg.com/bignumber.js/-/bignumber.js-9.0.1.tgz#8d7ba124c882bfd8e43260c67475518d0689e4e5"